Electro-optical inspection apparatus and method with dust or particle collection function

ABSTRACT

An electro-optical inspection apparatus is provided that is capable of preventing adhesion of dust or particles to the sample surface as much as possible. A stage ( 100 ) on which a sample ( 200 ) is placed is disposed inside a vacuum chamber ( 112 ) that can be evacuated to vacuum, and a dust collecting electrode ( 122 ) is disposed to surround a periphery of the sample ( 200 ). The dust collecting electrode ( 122 ) is applied with a voltage having the same polarity as a voltage applied to the sample ( 200 ) and an absolute value that is the same or larger than an absolute value of the voltage. Thus, because dust or particles such as particles adhere to the dust collecting electrode ( 122 ), adhesion of the dust or particles to the sample surface can be reduced. Instead of using the dust collecting electrode, it is possible to form a recess on a wall of the vacuum chamber containing the stage, or to dispose on the wall a metal plate having a mesh structure to which a predetermined voltage is applied. In addition, adhesion of dust or particles can be further reduced by disposing a gap control plate ( 124 ) having a through hole ( 124   a ) at the center above the sample ( 200 ) and the dust collecting electrode ( 122 ).

TECHNICAL FIELD

The present invention relates to an electro-optical inspection apparatusand method for inspecting a sample surface using an electron beam, andmore particularly, to an electro-optical inspection apparatus and methodthat is capable of inspecting a sample surface at high sensitivity usingan electron beam while preventing adhesion of dusts or particles tosample surfaces (of front and back sides and peripheral edges).

BACKGROUND ART

The electro-optical inspection apparatus is used for obtaining an imageof a sample surface of a semiconductor wafer or the like by irradiatingthe sample surface with a primary electron beam, and detecting secondaryelectrons or mirror electrons emitted from the sample surface, toperform inspection of defects on the sample surface and/or patternevaluation of the sample surface on the basis of the obtained image.

In addition, it is known that while a sample such as a semiconductorwafer is conveyed in the air or in vacuum for inspection or processing,if adhesion of dusts such as particles having a diameter of 100 nm orsmaller to the sample surface can be prevented to reduce adhesion ofdusts or particles to be killer defects on a pattern to the samplesurface, production yield can be greatly improved. In a semiconductor orLSI manufacturing process, if the killer defects are on the samplesurface, a width of wiring or insulation resistance becomes insufficientso that performance is significantly deteriorated. Therefore, it isnecessary to take measures against the killer defects, such ascorrection or detection of the defects.

In particular, the electro-optical inspection apparatus can provide ameasurement or inspection result with high accuracy by reducing adhesionof dusts or particles generated by the inspection apparatus to a samplesurface. Thus, a process of dusts or particle adhesion to the samplesurface can be identified and improved so that defects in an exposureprocess can be reduced, for example.

Conventionally, in relation to conveyance of samples, measures have beentaken for reducing generation of dusts or particles as much as possible.For instance, as to an air conveyance system, a mini-environment havinga high-performance filter and down flow is provided, and the airconveyance system is housed in the mini-environment. Further, a staticelectricity remover removes static electricity of the sample so as toprevent particles from adhering to the sample surface. In addition, in avacuum conveyance system for samples, control of fluctuation of pressureis performed by a load lock. However, it is usually difficult to reducedusts or particles having very small sizes, in particular, of 100 nm orsmaller.

In view of this problem, the applicant has proposed a method of removingdusts or particles from a sample surface (refer to Japanese PatentApplication Publication No. 2009-4161 (Patent Document 1)). In thismethod, the dusts or particles on the sample surface are detected, thesample is moved in a horizontal direction, a collection electrodedisposed close and opposite to the sample surface is charged to have thepolarity opposite to the charge polarity of the dusts or particles, andhence approaching dusts or particles are electro-statically attracted bythe xollection electrode. Thus, the dusts or particles on the samplesurface are detected, and the detected dusts or particles are removedfrom the sample surface.

In addition, there is also proposed a particle monitor (refer toJapanese Patent Application Publication No. 2010-56270 (Patent Document2)), in which particles floating in a plasma processing apparatus arecollected actively by a dusts or particle collecting electrode and areaccumulated in a specific place using a quadrupole linear trap or thelike so that the particles are detected electrically or by using laserscattered light.

As a design rule of LSI has become very fine, a size of dusts orparticles to be prevented from adhering to a sample surface has becomevery small. Adhesion of dusts or particles generated by an operation ofthe inspection apparatus to the sample surface has become a criticalproblem, and it is necessary to take a countermeasure.

However, in the conventional dusts or particle adhesion preventionmechanism, it is difficult to prevent dusts or particles such as fineparticles of 100 nm or smaller, for example, from adhering to the samplesurface. In particular, if a sample is placed on a stage or the like ina vacuum chamber for inspecting the sample surface by theelectro-optical inspection apparatus, there has been no considerationabout suppressing generation of dusts or particles from the apparatusitself.

The prior art described in Patent Document 1 detects that dusts orparticles have adhered to the sample surface, and afterward removes theadhered dusts or particles from the sample surface. Therefore,conventional example described in Patent Document 1 cannot prevent dustsor particles from adhering to the sample surface. In addition, in theprior art described in Patent Document 2, the dusts collecting electrodeis provided to the tip of the particle monitor, for collecting particlesfloating in the plasma processing apparatus. Therefore, adhesion ofparticles to the sample surface cannot be prevented.

In addition, there is a case that, when a vacuum chamber is evacuated,air flow causes static electricity, which electrifies dusts or particlesremaining in the vacuum chamber, and the electrified dusts or particlessuch as particles are electro-statically attracted by the sample surfaceto be inspected and adhere thereto so that the sample surface iscontaminated. A conventional vacuum chamber used for inspecting a samplesurface has no countermeasure against the electrostatic attraction ofdusts or particles remaining in the vacuum chamber to the samplesurface, and cleaning has been the only way to cope with such remainingparticles. Therefore, it is strongly required to prevent such remainingparticles in the vacuum chamber that could not be removed by cleaningfrom adhering to the sample surface.

The present invention has been made in view of the above-mentionedproblem, and a first object thereof is to provide a method of preventingas many dusts or particles as possible from adhering to a samplesurface, and an electro-optical inspection apparatus for inspecting asample surface using an electron beam while preventing as many dusts orparticles as possible from adhering to the sample surface.

Japanese Patent Application Publication No. 2005-235777 (Patent Document3) describes a method of observing a sample surface using anelectro-optical inspection apparatus. This conventional method utilizesgradation differences of an image generated in a part where an opendefect or a short defect exists. In the part where a defect such as anopen defect or a short defect exists, gradation differences appear inthe image, which never appear in a normal part. Therefore, in theconventional method, a wafer surface image obtained from a semiconductorwafer surface is compared with an original surface image (of a waferwithout any defect). If a gradation difference, which must not appearwhen using a normal wafer, appears in a part, it is determined that thepart has an open defect or a short defect.

However, in an observation method disclosed in Patent Document 3, thereis a problem that the gradation difference in an observation part isoriginally small depending on a structure or material of the sample tobe observed, and that it is difficult to detect a short defect or anopen defect in some cases.

In addition, particularly in the case of the open defect, the image ofthe part where the open defect exists becomes darker (blacker) than theimage of the normal part in one case, and becomes lighter (whiter) thanthat of the normal part in another case. Therefore, there has been aproblem that it is very difficult to detect a defect and/or to classifya type of the defect.

In view of this problem, the inventors of the present invention havestudied to provide a sample surface observation method that can obtain asample surface image having large gradation differences between a defectpart and a normal part in defect detection of a wiring structure and aclear difference between gray levels of white and black, so that adefect can be easily detected. As a result, the inventors of the presentinvention have found that the problem of the sample surface observationmethod disclosed in Patent Document 3 is due to simultaneous detectionof a short defect and an open defect in the same condition. Hence, theyhave proposed a new sample surface observation method (see JapanesePatent Application Publication No. 2009-87893 (Patent Document 4)).

Patent Document 4 discloses a sample surface observation method in whichan electron beam irradiates a sample surface on which a wiring patterncontaining insulation material and conductive material is formed, andhence electrons having structural information of the sample surface aredetected so that an image of the sample surface is obtained forobserving the sample surface. The sample surface is irradiated by theelectron beam in the state where the insulation material and theconductive material have the same luminance in the sample surface imageso that a part other than the insulation material and the conductivematerial can be easily and reliably detected. In addition, a pointhaving a luminance which is different from the luminance of theinsulation material and the conductive material in the sample surfaceimage is detected as an open defect on the sample surface, so that theopen defect can be easily and reliably detected.

In addition, Patent Document 4 also discloses a sample surfaceobservation method that can effectively detect a short defect, in whichan electron beam irradiates a sample surface in a state that a luminancedifference between the insulation material and the conductive materialbecomes maximum in the sample surface image, and hence the samplesurface image that facilitates distinction between the short defect andits surrounding part is obtained, so that the short defect can be easilyand reliably detected. In addition, a state that the luminancedifference becomes the maximum is determined in a mirror electron regionin which electrons having the structural information of the samplesurface become mirror electrons.

However, the inventors of the present invention have further studied amethod and apparatus that enables observation of a sample surface withhigh contrasts in a case where an insulation region and a conductiveregion are formed on the sample surface, and facilitates not onlydetection of a short defect or an open defect but also classification ofa type of the defect. As a result, the inventors of the presentinvention have reached a conclusion that the method disclosed in PatentDocument 4 still has room for improvement.

Therefore, a second object of the present invention is to provide asample observation method and apparatus that can achieve theabove-mentioned first object, and further enables high contrastobservation of a sample surface on which an insulation region and aconductive region are formed, and facilitates detection of a shortdefect or an open defect as well as classification of a type of thedefect, and to provide a sample inspection method and apparatus usingthe sample observation method and apparatus.

SUMMARY OF INVENTION

To achieve the first object, the invention provides an electro-opticalinspection apparatus for inspecting a surface of a sample using anelectron beam, which comprises:

an electron beam source;

a primary electro-optical system comprising at least a primary lens forinducing a primary electron beam emitted from the electron beam source;

a stage for mounting the sample thereon, the surface of the sample beingirradiated with the primary electron beam induced through the primaryelectro-optical system;

a secondary electro-optical system comprising at least a secondary lensand an aperture for defining NA (Numerical Aperture), for inducingsecondary electrons and mirror electrons, the secondary electrons beingemitted from the sample surface when irradiating the sample surface withthe primary electron beam, and the mirror electrons being reflected fromthe sample surface and its vicinity when irradiating the sample surfacewith the primary electron beam;

a detector for detecting at least either of the secondary electrons ormirror electrons induced through the secondary electro-optical system;

a first power source for supplying a first voltage to the sample mountedon the stage;

at lest a first electrode located to surround the sample mounted on thestage, for collecting dusts or particles; and

a second power source for supplying a second voltage to the firstelectrode, the second voltage having the same polarity as that of thefirst voltage and an absolute value which is equal to and larger thanthat of the first voltage.

In the above electro-optical inspection apparatus according to theinvention, it is preferable to further comprise at least a secondelectrode located to surround the first electrode, for collecting dustsor particles, and a third power source for supplying a third voltage tothe second electrode, the third voltage having the same polarity as thatof the first voltage and an absolute value which is equal to or largerthan that of the first voltage. In addition, it is preferable to furthercomprise a plate located over the sample mounted on the stage, to coverthe sample, the plate having an aperture through which an electron beampasses to/from the sample surface, and a cover surrounding the stage forpreventing dusts or particles from flowing to the stage.

In the above electro-optical inspection apparatus according to theinvention, it is preferable to further comprise a first terminal platecomprising at least two terminals, one of which is connected to thefirst power source and the other of which is connected to the secondpower source, a cable including two electrical wires, first ends of theelectrical wires being connected to the terminals of the first terminalplate, respectively, a box containing the terminal plate, a portion ofthe cable and a second electrode for collecting dusts or particles inthe box, the portion of the cable being supported as flexibly bending,and a second terminal plate fixed at the stage and comprising at leasttwo terminals connected to second ends of the electrical wires, theterminals being used to supply the first and second voltages to thesample and the first electrode, wherein a portion of the cable betweenthe box and the second plate is supported to extend linearly, and theflexibly bending portion in the box bends or extends as the stage ismoving.

To achieve the first object, the invention also provides anelectro-optical inspection apparatus for inspecting a surface of asample using an electron beam, which comprises:

an electron beam source;

a primary electro-optical system comprising at least a primary lens forinducing a primary electron beam emitted from the electron beam source;

a stage for mounting the sample thereon, the surface of the sample beingirradiated with the primary electron beam induced through the primaryelectro-optical system;

a secondary electro-optical system comprising at least a secondary lensand an aperture for defining NA (Numerical Aperture), for inducingsecondary electrons and mirror electrons, the secondary electrons beingemitted from the sample surface when irradiating the sample surface withthe primary electron beam, and the mirror electrons being reflected fromthe sample surface and its vicinity when irradiating the sample surfacewith the primary electron beam;

a detector for detecting at least ones of the secondary electrons andmirror electrons induced through the secondary electro-optical system;

a chamber capable of being evacuated and containing the stage therein;and

a device for performing electrolytic dissociation gases in the chamberduring a process of vacuuming the chamber to eliminate staticelectricity which exists on structures in the chamber and materials onthe structures.

To achieve the first object, the invention further provides anelectro-optical inspection apparatus for inspecting a surface of asample using an electron beam, which comprises:

an electron beam source;

a primary electro-optical system comprising at least a primary lens forinducing a primary electron beam emitted from the electron beam source;

a stage for mounting the sample thereon, the surface of the sample beingirradiated with the primary electron beam induced through the primaryelectro-optical system;

a secondary electro-optical system comprising at least a secondary lensand an aperture for defining NA (Numerical Aperture), for inducingsecondary electrons and mirror electrons, the secondary electrons beingemitted from the sample surface when irradiating the sample surface withthe primary electron beam, and the mirror electrons being reflected fromthe sample surface and its vicinity when irradiating the sample surfacewith the primary electron beam;

a detector for detecting at least ones of the secondary electrons andmirror electrons induced through the secondary electro-optical system;and

a chamber capable of being evacuated and containing the stage therein,inner walls of the chamber having at least a hole, or comprisingmesh-metallic plates attached thereto, the plates being supplied with apredetermined voltage.

In each of the above electro-optical inspection apparatuses according tothe invention, it is preferable that the electron beam source is adaptedto emit a primary electron beam a cross section of which has asubstantial area.

Further, in the electro-optical inspection apparatus according to theinvention, it is further preferable to comprise an energy control meansfor setting energy of the electron beam directing to the sample surfaceand energy supplied to the sample such that electrons directing from thesample surface to a detector within a transition band which containsmirror electrons and secondary electrons, and an aperture adjustmentmechanism for adjusting a location of at least an aperture on a planeperpendicular to an axis of a secondary electro-optical system of theinspection apparatus, so that electrons from a conductive materialregion of the sample surface and electrons from a nonconductive materialregion of the sample surface are selectively induced to the detector. Bythe apparatus comprising the energy control means and apertureadjustment mechanism, the second object of the invention can beachieved. That is, the apparatus enables high contrast observation of asample surface on which an insulation region and a conductive region areformed, and facilitates detection of a short defect or an open defect aswell as classification of a type of the defect, while achieving thefirst object.

In the electro-optical inspection apparatus comprising the apertureadjustment mechanism, it is preferable that the secondaryelectro-optical system of the inspection apparatus comprises a pluralityof apertures having different diameters, respectively, and the apertureadjustment mechanism selects one of the apertures and adjusts itslocation such that electrons from either of the conductive materialregion and the nonconductive material region pass through the selectedaperture to the detector.

When using a primary electron beam having the cross section with asubstantial area, it is preferable that the detector comprises EB-CCD(s)or EB-TDI(s).

To achieve the first object, the invention also provides a method ofinspecting a surface of a sample using an electro-optical inspectionsystem, comprising the steps of:

setting the sample on a stage;

supplying a first voltage to the sample on a stage;

supplying a second voltage to a first electrode located to surround thesample on the stage to collect dusts and particles, the second voltagehaving the same polarity as that of the first voltage and an absolutevalue which is equal to or larger than that of the first voltage;

emitting a primary electron beam from an electron beam source, andirradiating the sample surface with the electron beam through a primaryelectro-optical system; and

detecting, at a detector, at least ones of secondary electrons andmirror electrons, the secondary electrons being emitted from the samplesurface when irradiating the sample surface with the primary electronbeam, and the mirror electrons being reflected from the sample surfaceand its vicinity when irradiating the sample surface with the primaryelectron beam.

In the above method according to the invention, it is preferable furthercomprise the step of supplying a third voltage to a second electrodelocated to surround the first electrode, the third voltage having thesame polarity as that of the first voltage and an absolute value whichis equal to or larger than that of the first voltage.

To achieve the first object, the invention further provides a method ofinspecting a surface of a sample using an electro-optical inspectionapparatus, comprising the steps of:

setting the sample on a stage;

supplying a first voltage to the sample on a stage;

vacuuming a chamber containing the stage;

dissociating electrolyticaly gases in the chamber which have existedduring the step of vacuuming the chamber to eliminate static electricityon structures in the chamber and materials on the structures;

emitting a primary electron beam from an electron beam source, andirradiating the sample surface with the electron beam through a primaryelectro-optical system; and

detecting, at a detector, at least ones of secondary electrons andmirror electrons, the secondary electrons being emitted from the samplesurface when irradiating the sample surface with the primary electronbeam, and the mirror electrons being reflected from the sample surfaceand its vicinity when irradiating the sample surface with the primaryelectron beam.

In the above method according to the invention, it is preferable thatthe electron beam source emits a primary electron beam a cross sectionof which has a substantial area, and the method further comprises thesteps of setting energy of the electron beam directing to the samplesurface and energy supplied to the sample such that electrons directingfrom the sample surface to a detector are within a transition band whichcontains mirror electrons and secondary electrons, and adjusting alocation of an aperture defining NA (Numerical Aperture), on a planeperpendicular to an axis of the secondary electro-optical system of theinspection apparatus, so that electrons from a conductive materialregion of the sample surface and electrons from a nonconductive materialregion of the sample surface are selectively induced to the detector bythe adjustment.

In addition, it is preferable in this method that the secondaryelectro-optical system comprises a plurality of apertures havingdifferent diameters, respectively, and the step of adjusting comprisesthe steps of selecting one of the apertures, and adjusting a location ofthe selected aperture such that electrons from either of the conductivematerial region and the nonconductive material region pass through theselected aperture to the detector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an overview of an electro-opticalinspection apparatus to which the present invention can be applied;

FIG. 2 is a diagram illustrating an overview of a sample observationsystem of a first embodiment to which the present invention can beapplied;

FIG. 3 is a front vertical sectional view illustrating an overview of amain part of the electro-optical inspection apparatus of an embodimentof the present invention;

FIG. 4 is a cross sectional plan view of the structure in FIG. 3,illustrating a relationship among a stage, a sample, and a dustcollecting electrode of the first embodiment;

FIG. 5 is a plan view illustrating a relationship among a stage, asample, and dust collecting electrodes of a second embodiment accordingto the present invention;

FIG. 6 is a plan view illustrating a relationship among a stage, acircular sample, and a dust collecting electrode of a third embodimentaccording to the present invention;

FIG. 7 is a plan view illustrating a relationship among a stage, acircular sample, and dust collecting electrodes of a fourth embodimentaccording to the present invention;

FIG. 8 is an enlarged cross sectional view illustrating the sample, thedust collecting electrode, and a gap control plate according to thepresent invention;

FIG. 9 is a diagram illustrating details of the stage according to thepresent invention;

FIG. 10 is a diagram illustrating an overview of a wiring box and astage disposed in a vacuum chamber according to the present invention;

FIG. 11 is an enlarged cross sectional view of the sample, another dustcollecting electrode, and the gap control plate according to the presentinvention;

FIG. 12 is an enlarged cross sectional view of the sample, still anotherdust collecting electrode, and the gap control plate according to thepresent invention;

FIG. 13 is an enlarged cross sectional view of the sample, and stillanother dust collecting electrode according to the present invention;

FIG. 14 is an enlarged cross sectional view of the sample, still anotherdust collecting electrode, and the gap control plate according to thepresent invention;

FIG. 15 is a diagram illustrating a relationship of forces acting bydielectric polarization on a particle formed of insulation materialexisting in a uniform electric field between parallel electrode plates;

FIG. 16 is a diagram illustrating a relationship of forces acting bydielectric polarization on a particle formed of insulation materialexisting in an ununiform electric field between a flat electrode plateand another electrode;

FIG. 17 is a diagram illustrating a relationship of forces acting bydielectric polarization on a particle formed of insulation materialexisting in a uniform electric field between a flat electrode plate andanother electrode;

FIG. 18 is a schematic diagram illustrating another vacuum chamberprovided to the electro-optical inspection apparatus according to thepresent invention;

FIG. 19 is a perspective view illustrating an example of a wallconstituting a planar structure in the vacuum chamber according to thepresent invention;

FIG. 20 is a cross sectional view of the structure in FIG. 19;

FIG. 21 is a perspective view illustrating another example of the wallconstituting the planar structure in the vacuum chamber according to thepresent invention;

FIG. 22 is a cross sectional view of the structure in FIG. 21;

FIG. 23A is a diagram illustrating an example of a relationship betweenlanding energy of an imaging electron beam and material contrast in anobtained image, and illustrating an example of different images obtaineddepending on a landing energy band;

FIG. 23B is a graph illustrating an example of a relationship betweenlanding energy of an imaging electron beam and material contrast in anobtained image, and illustrating a correlation between landing energy ofthe imaging electron beam and detector current;

FIG. 24 is a diagram schematically illustrating an angle differencebetween a mirror electron having structural information of a samplesurface and a secondary electron, in which the horizontal axisrepresents effective landing energy (LE);

FIG. 25 is a graph illustrating a variation of gradation of the samplesurface with respect to the landing energy (LE);

FIG. 26A is a side view illustrating an example of a locus of anelectron having structural information of the sample surface;

FIG. 26B is a partially enlarged diagram illustrating an example of alocus of the electron having the structural information of the samplesurface viewed from an underside of a movable NA aperture;

FIG. 27A is a diagram illustrating an optimal position of an NA apertureplate for obtaining high material contrast in the case of the mirrorelectron;

FIG. 27B is a diagram illustrating an optimal position of the NAaperture plate for obtaining high material contrast in the case of thesecondary electron;

FIG. 28A is a diagram illustrating a cross sectional structure of asample having a contact plug structure;

FIG. 28B is a diagram illustrating an example of an obtained image of asample surface having a contact plug structure;

FIG. 29A is a table showing results of measurement of contrast whenlanding energy (LE) of the electron beam was changed to obtain a surfaceimage of the contact plug structure illustrated in FIG. 28A in aproduction test;

FIG. 29B is a graph plotting the results of measurement shown in FIG.29A;

FIG. 30A is a table of results of measurement showing a relationshipbetween a dose of a charged electron beam and contrast obtained by theproduction test;

FIG. 30B is a graph plotting the results of measurement shown in FIG.30A;

FIG. 31A is a table supplementarily showing that high contrast can beobtained by separating electrons (ec) having structural information of aconductive region from electrons (ei) having structural information ofan insulation region, and is a table of results of measurement showingdependence on the landing energy (LE) of secondary electron emissionefficiency and contrast of materials of the conductive region (Cu) andthe insulation region (SiO₂) in a case where the electrons (ec) havingthe structural information of the conductive region were not separatedfrom the electrons (ei) having the structural information of theinsulation region obtained by the production test;

FIG. 31B is a graph plotting the results of measurement shown in FIG.31A;

FIG. 32A is a table showing results of measurement of contrast when aratio of area (pattern width) between the conductive region and theinsulation region was changed on the sample surface by the productiontest, measured in an LEEM type and an SEM type using a low accelerationelectron beam apparatus;

FIG. 32B is a graph plotting the results of measurement shown in FIG.32A;

FIG. 33 is a diagram illustrating an example of a general structure ofthe electro-optical inspection apparatus according to the presentinvention;

FIG. 34A is a diagram illustrating an embodiment of a movable type NAadjustment aperture plate used in the electro-optical inspectionapparatus illustrated in FIG. 33;

FIG. 34B is a diagram illustrating another embodiment of the movabletype NA adjustment aperture plate used in the electro-optical inspectionapparatus illustrated in FIG. 33;

FIG. 35 is a diagram illustrating an example of a structure of adetector that is suitable for high resolution observation according tothe present invention;

FIG. 36A is a schematic diagram illustrating an image obtained in acondition where a luminance of the conductive region is higher than aluminance of the insulation region (Condition A), and conceptuallyillustrating manners in which the short defect and the open defectappear;

FIG. 36B is a schematic diagram illustrating an image obtained in acondition where the luminance of the insulation region is higher thanthe luminance of the conductive region (Condition B), and conceptuallyillustrating manners in which the short defect and the open defectappear;

FIG. 36C is a diagram schematically illustrating an image obtained byreversing contrast in the condition where the luminance of theinsulation region is higher than the luminance of the conductive region(Condition B), and conceptually illustrating manners in which the shortdefect and the open defect appear;

FIG. 37A is a schematic diagram illustrating an image obtained in thecondition where the luminance of the conductive region is higher thanthe luminance of the insulation region (Condition A), and conceptuallyillustrating manners in which the short defect and the open defectappear;

FIG. 37B is a schematic diagram illustrating an image obtained in thecondition where the luminance of the insulation region is higher thanthe luminance of the conductive region (Condition B), and conceptuallyillustrating manners in which the short defect and the open defectappear;

FIG. 37C is a diagram schematically illustrating an image obtained byreversing contrast in the condition where the luminance of theinsulation region is higher than the luminance of the conductive region(Condition B), and conceptually illustrating how the short defect andthe open defect appear;

FIG. 38A is a table showing results of measurement performed fordetermining an optimal value of landing energy (LE) of the imagingelectron beam irradiating the sample surface in the production test;

FIG. 38B is a graph plotting the results of measurement shown in FIG.38A;

FIG. 39A is a table showing results of measurement performed fordetermining an optimal value of dose of the charged electron beamirradiating the sample surface in the production test;

FIG. 39B is a graph plotting the results of measurement shown in FIG.39A;

FIG. 40A is a table showing results of measurement of positionconfirmation of electron distribution by an NA imaging mode, and showinga beam dose [mC/cm²] and a shift of a distribution state of the electron(ei) having surface structural information of the insulation materialwhen the charged electron beam of the dose irradiates, namely a shiftfrom a distribution state of the electron (ec) having surface structuralinformation of the conductive material;

FIG. 40B is a graph plotting the results of measurement shown in FIG.40A;

FIG. 41A is a table showing results of measurement performed fordetermining an optimal value of landing energy (LE) of the imagingelectron beam irradiating the sample surface in an electrified state,and showing the landing energy (LE), a luminance [DN] of each of theconductive material and the insulation material, and contrast;

FIG. 41B is a graph plotting the results of measurement shown in FIG.41A;

FIG. 42A is a table illustrating the reverse of contrast by NA apertureposition adjustment, and showing results of measurement of the luminance[DN] of each of the conductive material and the insulation material andcontrast when a center position of the NA aperture is moved from aposition substantially the same as the center of orbit of the electron(ec) emitted from the conductive region (normalized position=0) in Ydirection (to a normalized position=1.0);

FIG. 42B is a graph plotting the results of measurement shown in FIG.42A;

FIG. 43 is a diagram conceptually illustrating the reverse of contrastdue to the NA aperture position adjustment;

FIG. 44 is a flowchart illustrating, by means of an example, a procedureof determining dependence on the dose of the electron orbit shift, and aprocedure of confirming the reverse of material contrast, in a sampleobservation method of the present invention;

FIG. 45 is a flowchart illustrating, by means of an example, a procedureof the sample observation method of the present invention;

FIG. 46 is a flowchart illustrating another example of the procedure ofthe sample observation method of the present invention;

FIG. 47A is a table showing results of defect inspection performed bythe production test according to the method of the present invention,and showing whether or not a defect can be detected by the imageobtained in the condition where the luminance of the conductive regionis higher than the luminance of the insulation region;

FIG. 47B is a table showing results of defect inspection performed bythe production test according to the method of the present invention,and showing whether or not a defect can be detected by the imageobtained in the condition where the luminance of the insulation regionis higher than the luminance of the conductive region;

FIG. 47C is a table showing whether or not a defect can be detected as acombination of the defect detection results shown in FIGS. 47A and 47B;

FIG. 48 is a schematic diagram illustrating a structure for controllinga relationship among an acceleration voltage (Vacc), a retarding voltage(RTD), landing energy (LE), and a sample surface potential (ΔV) in theinspection of the sample surface according to the present invention;

FIG. 49 is a graph illustrating a relationship between mean luminance(meanDN) of the sample surface to be inspected and the landing energy(LE) according to the present invention;

FIG. 50 is a diagram illustrating a relationship between luminancedifference (ΔDN) of the sample surface to be inspected and a variationof surface potential according to the present invention;

FIG. 51 is a diagram illustrating examples (a) to (d) of imageinformation of the sample surface obtained when the landing energy (LE)to irradiate the sample surface is changed;

FIG. 52 is a graph illustrating a relationship between the landingenergy (LE) and the sample surface potential (ΔV) when the landingenergy (LE) to irradiate in advance the sample surface to be inspectedis changed according to the present invention;

FIG. 53A is a diagram illustrating an example of luminance distributionobtained when the sample surface is irradiated with landing energy (LE0)to be a reference and the landing energy (LE);

FIG. 53B is a diagram illustrating an example of determining samplesurface potential distribution (ΔV) from the luminance distributionillustrated in FIG. 53A;

FIG. 54 is a schematic perspective view illustrating an example in whichthe sample to be inspected is made of at least two materials;

FIG. 55A is a schematic diagram illustrating a model of transmittance ofelectrons through the sample in the thickness direction;

FIG. 55B is a schematic diagram illustrating a model of transmittance ofelectrons through the sample in the thickness direction;

FIG. 56 is a general schematic diagram illustrating a sample observationsystem of a second embodiment according to the present invention;

FIG. 57 is a general schematic diagram illustrating a sample observationsystem of a third embodiment according to the present invention; and

FIG. 58 is a flowchart illustrating an example of an adjustment methodof potential distribution on the sample surface according to the presentinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, with reference to the attached drawings, embodiments of thepresent invention are described.

FIG. 1 illustrates a structural example of an electro-optical inspectionapparatus to which the present invention can be applied. Thiselectro-optical inspection apparatus is a mapping projection type lowacceleration electron beam apparatus, which includes an electron beamsource 310, primary lenses 320, a condenser lens 330, electromagneticfield generation means (E×B) 340, a transfer lens 350, an NA adjustmentaperture plate 360 for adjusting a numerical aperture (NA), a projectionlens 370, a detector 400, an image processing device 500, a stage 100 onwhich a sample 200 to be observed is placed, and a landing energyadjust/supply unit 600.

At least one NA aperture 361 is formed in the NA adjustment apertureplate 360, and the NA aperture 361 determines the numerical aperture(NA). A position of the NA aperture 361 can be adjusted in a plane, andhence electrons having structural information of a conductive region andelectrons having structural information of an insulation region, whichare directed in different directions by the function of the E×B 340which will be described later, can be selectively guided to the detector400. Note that, this electro-optical inspection apparatus may have astructure including charged electron beam irradiation means 700 forirradiating the surface of the sample 200 with an electron beam toelectrify the sample surface as necessary.

The surface of the sample 200 has insulation and conductive regions, andobservation of the sample surface is performed by irradiating with anelectron beam from the electron beam source 310. The electron beamsource 310 includes, for example, an electron source 311, a Wehneltelectrode 312, and an anode 313. The electron source 311 generateselectrons, which are led out by the Wehnelt electrode 312 and areaccelerated by the anode 313 so that the sample surface is irradiatedwith the electrons.

The electron beam source 310 may have a structure to generate a surfaceelectron beam having a predetermined area including a plurality ofpixels so that a plurality of pixels can be imaged simultaneously. Thus,a plurality of pixels can be imaged simultaneously by one irradiation ofthe sample surface with the electron beam, and hence a two-dimensionalimage of a large area can be obtained at high speed.

The landing energy adjust/supply unit 600 is used to set landing energyof the electron beam emitted from the electron beam source 310. Thelanding energy adjust/supply unit 600 includes a variable voltage sourcehaving a negative electrode connected to the electron source andsupplies electric power to the electron beam source 310 so that theelectron source 311 generates electrons. The landing energy of theelectron beam is determined by a difference between a potential of thesample 200 and a potential of a cathode of the electron source 311 ofthe electron beam source 310. Therefore, the landing energyadjust/supply unit 600 can adjust the voltage of the variable voltagesource (hereinafter, referred to as an “acceleration voltage”) so thatthe landing energy can be adjusted.

In the electro-optical inspection apparatus according to the presentinvention, the landing energy adjust/supply unit 600 sets the landingenergy of the electron beam to an appropriate value, and contrast of anobtained image is enhanced. In the present invention, the landing energyof the electron beam is set in a transition region in which theelectrons having structural information of the surface of the sample 200by irradiation of the imaging electron beam include both the mirrorelectrons and the secondary electrons. A specific method of setting thelanding energy is described later.

Each of the primary lenses 320 deflects the electron beam emitted fromthe electron beam source 310 by an electromagnetic field, to therebyguide the electron beam to a desired irradiation region on the surfaceof the sample 200. Note that, there may be a plurality of primary lenses320 or a single primary lens 320. For example, a quadrupole lens can beused as each of the primary lenses 320.

The E×B deflector 340 applies an electric field and a magnetic field tothe electron beam or the electrons, and directing the electron beam orthe electrons by Lorentz force so that the electron beam or theelectrons are directed in a predetermined direction. The E×B deflector340 sets the electric field and the magnetic field so as to generate theLorentz force that directs the electron beam emitted from the electronbeam source 310 to the surface of the sample 200.

In addition, the E×B deflector 340 sets the electric field and themagnetic field so that the electrons having the structural informationof the sample surface by irradiation of the sample surface with theelectron beam propagate straight upward and are directed to thedirection of the detector 400. Aas described later, the electrons havingthe structural information of the sample surface emitted by irradiationof the sample surface with the imaging electron beam are directed by theelectric field and the magnetic field as the function of the E×Bdeflector 340 according to propagation speed of the electron beam in thedirection opposite to the incident direction.

By the function of the E×B deflector 340, it is possible to separate theelectron beam entering the sample surface from the electrons that aregenerated from the sample surface and propagate in the directionopposite to the incident electron beam. Note that, the E×B deflector maybe referred to as a Wien filter.

The condenser lens 330 is a lens that forms an image of the electronbeam on the surface of the sample 200 and condenses electrons havingstructural information of the sample surface. Therefore, the condenserlens 330 is disposed closest to the sample 200.

The transfer lens 350 guides the electrons after passing through the E×Bdeflector 340 to the direction of the detector 400 and forming acrossover in a vicinity of the NA aperture 361 of the NA adjustmentaperture plate 360.

The NA adjustment aperture plate 360 can adjust the number of passingelectrons. The NA adjustment aperture plate 360 has the NA aperture 361in the center portion, which is an aperture determining the numericalaperture (NA). The NA aperture 361 transmits the electrons that areemitted from the sample surface and are guided by the transfer lens 350,to be a passage to the detector 400. The NA aperture 361 can preventelectrons which may be noise in imaging, from propagating to thedetector 400 and adjusts the number of passing electrons. In addition,as described above, a position of the NA aperture 361 in the plane canbe adjusted, and hence electrons having structural information of aconductive region and electrons having structural information of aninsulation region, which are directed in different directions by thefunction of the E×B deflector 340, can be selectively guided to thedetector 400. Details thereof are described later. There may be disposeda plurality of types of the NA apertures 361 having different aperturediameters. In this case, an NA aperture having a desired aperturediameter is selected by an NA aperture moving mechanism (not shown).

The projection lens 370 is final focus adjusting means for forming animage of electrons that have passed the NA adjusting aperture 361 on adetection surface of the detector 400.

The detector 400 detects electrons having structural information of thesample surface when the electron beam irradiates the sample surface soas to obtain an image of the sample surface. Various detectors can beused as the detector 400. For example, a charge coupled device (CCD)detector capable of obtaining parallel images or a time delayintegration (TDI)-CCD detector can be used. Using a two-dimensionalimaging type detector 400 such as a CCD or a TDI-CCD, and using asurface beam that can irradiate a predetermined area including aplurality of pixels as the electron beam source 310, it is possible toobtain an image of wide area by parallel imaging with beam irradiationin one spot so that the sample surface can be observed at high speed.The CCD or the TDI-CCD is a detection element that detects light andoutputs an electric signal. If the CCD or the TDI-CCD is used as thedetector 400, a fluorescent screen that converts electrons into light ora micro channel plate (MCP) that multiplies electrons is necessary andshould be included in the detector 400.

An EB-CCD or an EB-TDI may be used as the detector 400. The EB-CCD andthe EB-TDI are two-dimensional imaging type detectors similarly to theCCD and the TDI-CCD, but directly detect electrons and output theelectric signal as it is without conversion between light and electrons.Therefore, the above-mentioned fluorescent screen or MCP is notnecessary, and a signal loss in the process is reduced so that an imagewith high resolution can be obtained.

The image processing device 500 is a device that stores the electricsignal output from the detector 400 and generates an image of thesurface of the sample 200 based on the stored signal. Specifically, atwo-dimensional image is generated based on coordinate information andluminance information output from the detector 400. In order to observethe sample 200 having the surface containing insulation material andconductive material, it is preferred that a luminance difference begenerated between the insulation region and the conductive region sothat an image with high contrast is obtained. The image processingdevice 500 performs necessary image processing and image generation sothat a good image can be obtained.

The stage 100 has an upper surface on which the sample 200 placed sothat the sample 200 is supported. The stage 100 can be moved in the Xdirection and in the Y direction of the horizontal plane (X-Y plane) andcan be rotated in the horizontal plane so that the electron beam canirradiate the entire region to be observed of a sample surface 201. Inaddition, it is possible to constitute the stage 100 to be movable inthe vertical direction (Z direction) as necessary so that a height ofthe surface of the sample 200 can be adjusted. In order to constitutethe stage 100 to be movable, for example, moving means such as a motoror an air actuator should be disposed.

The charged electron beam irradiation means 700 is provided forelectrifying the sample 200 before the sample 200 is irradiated with theimaging electron beam for imaging from the electron beam source 310. Thecharged electron beam irradiation means 700 is provided as necessary.Assuming that the sample surface is irradiated with the electron beam inadvance before imaging of the sample surface, the conductive region isnot electrified so that the potential thereof remains to be the groundpotential, while the insulation region is negatively electrified.Therefore, it is possible to form a potential difference between theconductive region and the insulation region according to theirmaterials. Then, the potential difference can enhance the contrastbetween the conductive region and the insulation region. Therefore, ifit is desired to irradiate the sample surface with the charged electronbeam before the imaging electron beam irradiates, the charged electronbeam irradiation means 700 should be disposed.

It is possible that the electron beam source 310 works also as thecharged electron beam irradiation means without separately providing thecharged electron beam irradiation means 700. In other words, the chargedelectron beam may be irradiated from the electron beam source 310instead of using the charged electron beam irradiation means 700. Then,after irradiation with the charged electron beam, the surface of thesample 200 may be irradiated with the electron beam for imaging.

Therefore, charged electron beam irradiation means 700 may be disposed,for example, in the case where the charged electron beam shouldirradiate the sample surface 201 and the electron beam for imagingshould be irradiated promptly after the irradiation with the chargedelectron beam. In general, the imaging electron beam and the chargedelectron beam have different landing energy. By disposing the chargedelectron beam irradiation means 700, adjustment of landing energybetween the charged electron beam irradiation and the imaging electronbeam irradiation becomes unnecessary so that the imaging can beperformed promptly. Therefore, if there is high requirement for reducingobservation time, the charged electron beam irradiation means 700 shouldbe disposed to satisfy the requirement for reducing observation time.

The surface of the sample 200 usually includes an insulation region madeof insulation material and a conductive region made of conductivematerial. Samples 200 having various shapes can be used. For instance, awafer-like sample such as a semiconductor wafer or a reticle is used. Itis preferred that the electro-optical inspection apparatus according tothe present invention have a structure in which the sample surface canbe observed appropriately also in the case where an area ratio of theinsulation region to the sample surface is larger than that of theconductive region. With this structure, an image of the sample surfacecan be obtained and observed appropriately also for a contact plug of asemiconductor wafer or a contact structure of a reticle, for example.

Various materials can be used as the conductive material or theinsulation material. For instance, plug material such as tungsten (W)can be used as the conductive material, and silicon oxide film (SiO₂)that is used as an insulation layer of a semiconductor wafer can be usedas the insulation material.

The electro-optical inspection apparatus illustrated in FIG. 1 is themapping projection type electro-optical inspection apparatus asdescribed above, but an SEM type electro-optical inspection apparatuscan also be used as the electro-optical inspection apparatus of thepresent invention.

FIG. 2 is a diagram illustrating a general structural example of asample observation system (inspection system) of the first embodimentincluding an electro-optical inspection apparatus according to thepresent invention. This sample observation system is constituted as acombination type sample observation system capable of observing a samplewith the mapping projection type electro-optical system and an opticalmicroscope and of observing a sample with the SEM type electro-opticalsystem.

The combination type sample observation system illustrated in FIG. 2includes a load port 1900, a mini-environment 1800, a load lock 1620, atransfer chamber 1610, a main chamber 1600, a mapping projection typeelectro-optical system 1300, and the image processing device 500. Themini-environment 1800 is provided with an air conveyance robot, a samplealignment device, a clean air supply mechanism, and the like (notshown). In addition, the transfer chamber 1610 that is always in avacuum state is provided with a vacuum conveyance robot (not shown),which can suppress occurrence of particles due to pressure fluctuationto a minimum level.

The main chamber 1600 is provided with the stage 100 that can move inthe X direction, in the Y direction, and in θ (rotational) direction inthe horizontal plane (XY plane). On the stage 100, there is disposed anelectrostatic chuck (denoted by 120 in FIG. 3). The sample itself or thesample placed on a palette or a jig is placed on the stage 100 by theelectrostatic chuck.

The inside pressure of the main chamber 1600 is controlled by a vacuumcontrol system 1500 so that the vacuum state is maintained. In addition,the main chamber 1600, the transfer chamber 1610, and the load lock 1620are placed on a vibration isolation table 1700 so that vibration is nottransmitted from the floor.

The main chamber 1600 is provided with the electro-optical system 1300.This electro-optical system 1300 is equipped with a primary opticalsystem including the electron beam source 310 and the primary lens 320illustrated in FIG. 1, a secondary optical system including thecondenser lens 330, the E×B deflector 340, the transfer lens 350, the NAadjustment aperture plate 360, and the projection lens 370, and thedetector 400 for detecting secondary electrons and mirror electrons fromthe sample 200. In addition, as elements related to the electro-opticalsystem 1300, there are disposed an optical microscope 1400 that is usedfor alignment of the sample, and an SEM 1450 that is used for reviewobservation.

A signal from the detector 400 is sent to the image processing device500 for signal processing. The signal processing can be performed bothin real time process for a currently observed image and in off lineprocess in which an image is obtained and is later processed. The dataprocessed by the image processing device 500 is stored in a recordingmedium such as a hard disk or a memory. In addition, it is possible todisplay on a monitor of a console as necessary, for example, as anobservation region, a defect map, a defect classification, a patchimage, and the like. In order to perform the signal processing, there isdisposed a system control part 950. In addition, in order to supplyelectric power to the electro-optical system 1300, there is disposed anelectro-optical system control power supply 1180. The electro-opticalsystem control power supply 1180 includes a power supply 600 forsupplying electric power to the electron source 311 of the electron beamsource 310, and landing energy control means for controlling the powersupply. The electro-optical system control power supply 1180 alsoincludes a power supply for setting a potential of the sample, which isdescribed later, and control means thereof, and a power supply for avoltage to be applied to a dust collecting electrode, which is describedlater, and control means thereof.

Next, a conveyance mechanism for the sample is described. The samplesuch as a wafer or a mask is conveyed from the load port 1900 to themini-environment 1800, in which alignment is performed. Further, thesample is conveyed by the air conveyance robot to the load lock 1620. Inthe load lock 1620, air is exhausted by a vacuum pump (not shown) fromthe atmospheric state to a vacuum state. When the pressure inside theload lock 1620 becomes a predetermined pressure (for example,approximately 1 Pa) or lower by this exhaustion, the sample is conveyedfrom the load lock 1620 to the main chamber 1600 by the vacuumconveyance robot disposed in the transfer chamber 1610 and is placed onan electrostatic chuck mechanism of the stage 100.

In the system of FIG. 2, the sample 200 is placed on the stage 100 thatis common to the mapping projection type electro-optical apparatus,namely the electro-optical system 1300, and the SEM type electro-opticalsystem 1450. Therefore, when the sample 200 moves between the mappingprojection type electro-optical system 1300 and the SEM typeelectro-optical system 1450, the coordinate relationship is uniquelydetermined so that the same part can be identified easily with highaccuracy.

In other words, when the sample is moved between separate inspectionapparatuses, it is necessary to place the sample on separate stages.Therefore, it is necessary to perform alignment of the sampleindividually, and even if the sample alignment is performed in this way,specific error of the same place becomes 5 to 10 μm or larger. Inparticular, if the sample has no pattern, a position reference cannot bespecified so that the error is further increased.

According to this example, if the sample 200 moves between the mappingprojection type electro-optical system 1300 and the SEM typeelectro-optical system 1450, the same place can be identified with highaccuracy. Therefore, a place can be identified with high accuracy, forexample, an accuracy of 1 μm or smaller. Thus, if the inspection of apattern and a pattern defect is performed by the mapping projection typeelectro-optical system 1300, it is very effective to performidentification and detailed observation (review) of the detected defectwith the SEM type electro-optical system 1450. In other words, because aplace can be identified, it is possible to detect presence or absence ofdefect (pseudo-detection in the case of absence), and accurate size andshape of the defect can be detected at high speed. If separateapparatuses are used, detection of a pattern defect and identificationthereof take much time.

According to the present invention, because a system in which themapping projection type electro-optical system and the SEM typeelectro-optical system are disposed in the same chamber, is used, it ispossible to perform inspection, decision, and classification of anultrafine pattern of 100 nm or smaller, in particular, with highefficiency and at high speed.

Next, with reference to FIGS. 3 to 23, the structure for preventing dustor particles such as particles from adhering to a sample surfaceaccording to the present invention is described in detail. In theexample described below, a rectangular mask or a circular semiconductorwafer having a conductive thin film, for example, Si (including dope),Cr, TaN, TaBN, CrN, Ru, Ta, W, or Cu thin film as a surface layer isused as the sample 200. The uppermost surface of the thin film may be aninsulation film made of TaBO, TaO, SiO₂, or the like. In addition, themask may be constituted of a quartz substrate on which a thin film isformed, for example, or a Si wafer on which a circuit pattern filmstructure for LSIs is formed.

FIG. 3 is a front vertical cross sectional view that illustrates indetail the stage 100 and its peripheral portions of the electro-opticalinspection apparatus according to the present invention illustrated inFIG. 1. FIG. 4 is a cross sectional plan view of FIG. 3. As illustratedin FIGS. 3 and 4, the electro-optical inspection apparatus according tothe present invention includes a vacuum chamber 112 that can performvacuum evacuation. Inside the vacuum chamber 112, there is disposed thestage 100 that can move in the X direction and in the Y direction. Then,on the upper surface of the stage 100, in this example, a holder 118holding the sample 200, which is a rectangular mask, is placed via theelectrostatic chuck 120.

The stage 100 has a stroke movement region of an effective distance ofthe sample 200 plus a run-up distance (inspection maximum speed×speedstabilization time) so that imaging of an effective region of the sample(mask) 200 and the defect inspection can be performed. For instance,supposing that the effective distances of the sample 200 in the Xdirection and in the Y direction are 300 mm each, and the run-updistance is 50 mm (=100 mm/s×0.5 sec), the stage 100 has the strokemovement region of 400 mm.

A dust (or particle) collecting electrode 122 that has a rectangularcross section and extends continuously in a shape of a rectangular frameis disposed at a position surrounding the entire periphery of the sample200 with a predetermined interval between the dust collecting electrode122 and the sample 200 placed on the stage 100. Further, a gap controlplate 124 having a center through hole 124 a is disposed above thesample (mask) 200 placed on the stage 100 and the dust collectingelectrode 122 in a horizontal posture with a small gap between the innersurface of the vacuum chamber 112 and the gap control plate 124. In thisthrough hole 124 a, there is an optical system element, namely thecondenser lens 330 of the electro-optical inspection apparatus. Theelectron beam is irradiated through this condenser lens 330 to thesurface of the sample 200 placed on the stage 100. A size of the throughhole 124 a is set to be slightly larger than the outside shape of thecondenser lens 330.

The dust collecting electrode 122 is made of non-magnetic material suchas phosphor bronze or Ti so as to eliminate a curve of the electron beamor a change of orbit due to the magnetic field. The electron beamincludes a primary irradiating electron beam, a secondary emissionelectron beam emitted from the sample 200, a mirror electron beamreflected in a vicinity of the sample 200, and the like.

The gap control plate 124 is made of phosphor bronze, Ti, or SUS sheethaving a thickness of 0.3 to 5 mm, for example. It is preferred that thegap control plate 124 be coated with Au, Pt, Ru, or Os so that thepotential is stabilized and contamination is prevented. Further, the gapcontrol plate 124 has a size that is set so that the dust collectingelectrode 122 covers a region that does not go out of the region of thegap control plate 124 when the stage 100 moves within its movementregion. Thus, it is prevented that the electric field distribution isdisturbed and that the orbit of the particle changes when the stage 100moves and the sample 200 placed on the stage 100 moves to the mostdistant position in the vacuum chamber 112. Thus, it is possible toprevent the particles from moving to the sample 200 and adhering to thesample surface. Note that, the gap control plate 124 is not alwaysnecessary. The same is true in the following examples.

In this example, as illustrated in FIG. 4, the dust collecting electrode122 that is continuous in a shape of a rectangular frame is used, andthe entire periphery of the sample 200 placed on the stage 100 issurrounded integrally by the dust collecting electrode 122. Thus, it ispossible to prevent particles from entering the inside surrounded by thedust collecting electrode 122 through a so-called electric field gapwhen a gap occurs at a position along a length direction of the dustcollecting electrode 122 so that an uneven part of the electric fieldoccurs.

It is not always necessary that the dust collecting electrode 122surrounds the entire periphery of the sample 200. It is sufficient thatthe electric field formed by the dust collecting electrode 122 cansurround the periphery of the sample 200. For instance, as illustratedin FIG. 5, four dust collecting electrodes 122 a extending linearly maybe disposed along substantially the entire length of the individualsides of the sample 200 so that the dust collecting electrodes 122 asurround substantially the entire periphery of the sample 200 except forthe vicinities of the corners. Alternatively, though not illustrated, itis possible that the dust collecting electrodes extending linearly areseparated from each other at a mid position. In this case, a distortionof electric field occurs between adjacent dust collecting electrodes,but it is sufficient if necessary potential distribution is obtained bythe dust collecting electrode. For instance, in a two-dimensional case,when a width of the dust collecting electrode is denoted by D, and adistance between dust collecting electrodes is denoted by L, there is noproblem if D/L≧4 is satisfied. The same is true in the followingexamples.

In the examples illustrated in FIGS. 3 to 5, the rectangular mask isused as the sample 200. When the circular semiconductor wafer is used asthe sample, a circular sample (semiconductor wafer) 200 a held by acircular holder 118 a is placed on the stage 100 as illustrated in FIG.6, and a dust collecting electrode 122 b that is continuous in a shapeof a ring is disposed around the sample so that the entire periphery ofthe sample 200 a is surrounded integrally. In this case, as illustratedin FIG. 7, it is possible to dispose a pair of semicircular dustcollecting electrodes 122 c to be opposed to each other to form acircle, to thereby surround substantially the entire periphery of thecircular sample (semiconductor wafer) 200 a placed on the stage 100 bythe dust collecting electrodes 122 c. In addition, though notillustrated, it is possible to dispose three or more dust collectingelectrodes extending along circumferential direction of a circle with aspace between adjacent dust collecting electrodes.

In any case, a predetermined voltage is applied to all of one or moredust collecting electrodes 122 surrounding the sample 200 placed on thestage 100 so as to collect dust, and afterward the electron beam source310 (see FIG. 1) generates the electron beam, which irradiates thesample 200 on the stage 100. Thus, secondary electrons emitted from thesample or mirror electrons reflected from the sample surface and itsvicinity are detected by the detector 400 (see FIG. 1), and the imageprocessing device 500 performs image processing so that an image of thesample surface is obtained.

FIG. 8 is an enlarged view of the sample 200, the dust collectingelectrode 122, and the gap control plate 124. As illustrated in FIG. 8,the sample 200 is connected to a first power supply 128 for applying apredetermined voltage to the sample surface, and the dust collectingelectrode 122 is connected to a second power supply 130 for applying apredetermined voltage to the dust collecting electrode. A thickness ofthe dust collecting electrode 122 is 0.1 to 5 mm, for example. It isbetter as a width W1 of the dust collecting electrode 122 is larger.However, as the width W1 of the dust collecting electrode 122 is larger,a size of the dust collecting electrode 122 occupying the space in thevacuum chamber 112 becomes larger. Therefore, the width W1 of the dustcollecting electrode 122 is usually set to 5 to 50 mm. A distance L1between the sample 200 and the dust collecting electrode 122 is relatedto the width W1 of the dust collecting electrode 122, and it ispreferred that the relationship of 0.5L1<W1<5L1 be satisfied, forexample.

In this example, a voltage of −1 to −5 kV is applied to the surface ofthe sample 200 via the first power supply 128, and a voltage having thesame polarity as the voltage applied to the sample 200 and an absolutevalue larger the voltage applied to the sample 200 by 0.5 to 5 kV, forexample, is applied to the dust collecting electrode 122 via the secondpower supply 130. In other words, when a voltage of, for example, −3 kVis applied to the sample 200, a voltage of −3.5 to −8 kV, for example,−5 kV is applied to the dust collecting electrode 122.

The vacuum chamber 112 is made of metal such as iron or aluminum, andhas the ground potential. Further, when dust or particles such asparticles existing inside the vacuum chamber 112 are electrified bystatic electricity or the like, if a potential of the sample 200 isnegative, the dust or particles such as particles that are positivelyelectrified are attracted by the electric field and move toward thesample 200.

According to this example, the entire periphery of the sample 200 towhich a negative potential is applied is surrounded by the dustcollecting electrode 122, and a voltage more negative than the voltageapplied to the sample 200 is applied to the dust collecting electrode122. Therefore, most undesired objects such as dust or particlesattracted by the electric field can be trapped by the dust collectingelectrode 122. Thus, a probability that the dust or particles such asparticles reach the sample 200 and adhere to the sample surface can belargely reduced. In this way, adhesion of dust or particles to thesurface of the sample 200 can be reduced largely.

In this example, the gap control plate 124 is further disposed, whichprevents dust or particles such as particles from moving along an orbitdistant from the dust collecting electrode 122 and adhering to thesurface of the sample 200. By disposing the gap control plate 124,attraction force of the dust collecting electrode 122 for dust orparticles such as particles moving along an orbit distant from the dustcollecting electrode 122 is decreased, and for this reason, aprobability that the dust or particles such as particles are trapped bythe dust collecting electrode 122 is decreased in inverse proportion toa distance. In order to prevent the decrease of probability of trappingthe dust or particles, when a negative voltage is applied to the sample200, electric field intensity A between the sample 200 and the dustcollecting electrode 122 is set to be negative (A<0). Thus, attractionforce of the dust collecting electrode 122 is increased, and hence theprobability that the dust collecting electrode 122 traps the dust orparticles such as particles can be increased. In addition to that,electric field intensity (absolute value) B between the gap controlplate 124 and the dust collecting electrode 122 is adjusted so that0.1≦B (absolute value)≦10 kV/mm is satisfied. Thus, the probability thatthe dust collecting electrode 122 traps the dust or particles such asparticles can be further increased.

For instance, a negative voltage of −1 to −5 kV is applied to the sample200, and a negative voltage of −1.5 to −10 kV that is more negative thanthe negative voltage applied to the sample 200 by −0.5 to −5 kV isapplied to the dust collecting electrode 122. It is supposed that thegap control plate 124 has the ground potential, the distance L1 betweenthe sample 200 and the dust collecting electrode 122 is 10 mm, and adistance Z1 between the gap control plate 124 and the dust collectingelectrode 122 is 8 mm. Then, the electric field intensity A between thesample 200 and the dust collecting electrode 122 becomes negative (A<0),and the electric field intensity (absolute value) B between the gapcontrol plate 124 and the dust collecting electrode 122 becomes 0.19 to1.25 kV/mm (=1.5 to 10 kV/8 mm). In particular, when a voltage of −5 kVis applied to the dust collecting electrode 122, the electric fieldintensity (absolute value) B becomes 0.625 kV/mm (=5 kV/8 mm), which isan effective condition. In this case, the voltage is set not to exceed10 kV/mm as a withstand voltage of the space so that occurrence ofdischarge in the space can be prevented.

FIG. 9 illustrates details of the stage 100. As illustrated in FIG. 9,the stage 100 is constituted of an X stage 132 and a Y stage 134 thatare stacked on each other. An ultrasonic motor 136 is disposed betweenthe X stage 132 and the Y stage 134. In a position surrounding theoutside of the dust collecting electrode 122 on the upper surface of thestage 100, there is disposed a first dust cover 140 whose upper edgereaches above the dust collecting electrode 122, and there is disposed asecond dust cover 142 on the outside of the ultrasonic motor 136 so asto close an open end of a housing portion for the ultrasonic motor 136.

By disposing the first dust cover 140 is disposed, it is possible toprevent dust or particles such as particles from scattering toward thesurface of the sample 200 and adhering to the sample surface. Inaddition, by disposing the second dust cover 142 on the outside of theultrasonic motor 136 to be a source of particles, it is possible toprevent dust or particles such as particles scattering from theultrasonic motor 136 from entering inside the vacuum chamber 112.Prevention of dust or particles such as particles from scattering fromthe source thereof to the inside of the vacuum chamber 112 is effectiveparticularly in the case where a wall friction drive type motor such asa Piezo-actuator is used.

In this example, as illustrated in FIG. 10 in detail, a wiring box 150having an airtight structure is disposed inside the vacuum chamber 112.This wiring box 150 is used for preventing undesired objects such asparticles generated from cables due to bending or friction of the cablesfrom scattering inside the vacuum chamber 112. In this example, portionsof cables 152 that are bent accompanying movement of the stage 100 onwhich the sample 200 is placed are all housed inside the wiring box 150.More specifically, the power supply for applying a predetermined voltageto the sample 200 (800 illustrated in FIGS. 1, and 128 illustrated inFIGS. 11 to 14) and the power supply for applying a predeterminedvoltage to the dust collecting electrode 122 (130 illustrated in FIGS.11 to 13) are disposed outside the wiring box 150. These external powersupplies and a terminal strip 156 are electrically connected via a cable(not shown) extending from the terminal strip 156 and a feed-throughdisposed in the vacuum chamber 112. The terminal strip 156 includes twopairs of terminals for applying power supply voltages to the sample andto the dust collecting electrode. In addition, the cable 152 includestwo pairs of power supply lines for transferring power supply voltages,and one end of each of the two pairs of power supply lines is connectedelectrically to corresponding one of the two pairs of terminals of theterminal strip 156. Note that, one end of the cable 152 is mechanicallyfixed to a movement plate 158 disposed in a vicinity of the terminalstrip 156 in a movable manner as illustrated in the figure. A length ofthe cable between the movement plate 158 and the terminal strip 156 hasa margin in view of a movement range of the movement plate 158. On theother hand, a fixing plate 154 is fixed to the stage 100, and the fixingplate also includes two pairs of terminals for applying voltages to thesample and the dust collecting electrode. These terminals areelectrically and mechanically connected to the corresponding powersupply lines of the cable 152.

Further, as illustrated in the figure, the cable 152 connected to thefixing plate 154 fixed to the stage 100 extends linearly from the stage100 to the wiring box 150, passes through a slit 150 a provided to thewiring box 150 to enter the inside of the wiring box 150, and then turnsdownward and is reversed by 180 degrees. Then, as described above, theother end of the cable 152 is mechanically fixed to the movement plate158 disposed inside the wiring box 150, and the tip thereof is connectedto the terminal strip 156. Thus, when the stage 100 moves in the Xdirection, the cable 152 is bent only at the flexion part 152 a in thewiring box 150.

Inside the wiring box 150, there is disposed guide rollers 160 extendingin the Y direction (perpendicular to the paper plane of FIG. 10) so asto guide the cable 152. When the stage 100 moves in the Y direction, thecable 152 moves along the guide rollers 160 in the Y direction, andhence the movement plate 158 moves. Therefore, a stress in the Ydirection is not applied to the cable 152 extending to the movementplate 158.

Note that, the movement plate 158 is disposed in a movable manner in theabove-mentioned embodiment, but it is possible to absorb a variation ofthe cable 152 due to movements of the stage 100 in the X direction andin the Y direction only by expansion and contraction of the flexion part152 a of the cable 152. Then, a fixing plate may be used instead of themovement plate to fix the cable 152 mechanically.

In this way, the bending part of the cable 152 is entirely inside thewiring box 150, and the hole communicating inside and outside of thewiring box 150 is small. Therefore, the probability that dust orparticles generated in the wiring box 150 go outside the wiring box 150is significantly decreased, and most of the dust or particles adhere tothe inner wall of the wiring box 150. Further, in this example, a dustcollecting electrode 162 for wiring box is disposed inside the wiringbox 150, and a voltage for attracting the dust or particles is appliedto the dust collecting electrode 162. Thus, the probability that thedust or particles such as particles scatter from the wiring box 150 tothe outside can be reduced more.

It is possible to take measures of (1) using cables of equal length, (2)fixing and correcting cables with an insulock tie or the like, or (3)using a flat cable as cables. Thus, generation of particles due tofriction among cables can be reduced. In other words, when a pluralityof cables of equal length are fixed, the cables become one bunch. Whenthe stage moves, flexion occurs in the cables. In this case, frictionamong cables can be reduced so that occurrence of dust or particles suchas particles can be reduced. Alternatively, if a flat cable is usedinstead of the cables, a plurality of wires can be replaced by one cableso that friction among cables can be eliminated. If a flat cable havingmany wires is not immediately available, it is effective to combine theabove-mentioned (1) and (2).

In the example described above, the dust collecting electrode 122 havinga rectangular cross section is used, but a dust collecting electrode 122d having a circular cross section may be used as illustrated in FIG. 11.A diameter D of this dust collecting electrode 122 d is related to adistance L2 between the sample 200 and the dust collecting electrode 122d, and it is preferred to satisfy the relationship 0.5L2<D<5L2. If thediameter D of the dust collecting electrode 122 d is smaller than 0.5L2,the trapping probability of the dust collecting electrode 122 d isdecreased. If the diameter D of the dust collecting electrode 122 d islarger than 5L2, the trapping probability of the dust collectingelectrode 122 d does not change, and the trapping of excessive dust orparticles such as particles may be induced in some cases.

In addition, in the above-mentioned example, the dust collectingelectrode 122 is disposed at a position having a predetermined intervalfrom the sample 200, and a voltage having the same polarity as thevoltage applied to the sample 200 and an absolute value larger than thevoltage applied to the sample 200 is applied to the dust collectingelectrode 122. However, as illustrated in FIG. 12, it is possible todispose a dust collecting electrode 122 e that has a rectangular crosssection so that the inner edge portion thereof contacts with the outeredge portion of the sample 200, and is continuous in a shape of arectangular frame so as to surround the entire periphery of the sample.Further, a voltage that is the same as the voltage applied to the sample200 via the first power supply 128 may be applied to the dust collectingelectrode 122 e via the second power supply 130. A thickness of thisdust collecting electrode 122 e is 0.1 to 5 mm, for example, and a widthW2 is the same as that of the above-mentioned dust collecting electrode122, for example, 5 to 50 mm.

In the example illustrated in FIG. 12, the dust collecting electrode 122e having an inner shape smaller than an outer shape of the sample 200 isused so that the inner edge portion of the dust collecting electrode 122e contacts with the outer edge portion of the sample 200. However, asillustrated in FIG. 13, it is possible to use a dust collectingelectrode 122 f in a shape of a rectangular frame having an inner shapeslightly larger than an outer shape of the sample 200 and to dispose thedust collecting electrode 122 f so as to surround the entire peripheryof the sample 200 with a slight gap S between the dust collectingelectrode 122 f and the sample 200. This gap S is 1 to 500 μm, forexample.

In the example illustrated in FIG. 12, a voltage of −1 to −5 kV isapplied to the sample 200 via the first power supply 128, and a voltagethat is the same as the voltage applied to the sample 200 is applied tothe dust collecting electrode 122 e via the second power supply 130. Inother words, when a voltage of, for example, −3 kV is applied to thesample 200, a voltage of −3 kV is applied to the dust collectingelectrode 122 e.

Similarly to the above-mentioned example, if a potential of the sample200 is negative, the dust or particles that are positively electrifiedare attracted by the electric field and move toward the sample 200.According to the example illustrated in FIG. 12, because the dustcollecting electrode 122 e having the same potential as the sample 200is disposed to surround the entire periphery of the sample 200, most ofthe dust or particles, which are attracted by the electric field andmove toward the sample 200, are trapped by the dust collecting electrode122 e. In this way, because the dust collecting electrode 122 e disposedaround the sample 200 can trap most of the dust or particles, it ispossible to reduce dust or particles that scatter to the surface of thesample 200 and adhere to the sample surface. Thus, it is possible toprevent the dust or particles from adhering to the surface of the sample200.

In the example of FIG. 12, the distance between the dust collectingelectrode 122 e and the gap control plate 124 is denoted by Z2, and interms of a relationship between Z2 and the width W2 of the dustcollecting electrode 122 e, the effect becomes large particularly whenW2>4Z2 is satisfied. In addition, the effect becomes even larger when avalue of voltage density B (absolute value) between the dust collectingelectrode 122 e and the gap control plate 124 is larger than 0.1 kV/mm(B (absolute value)>0.1 kV/mm).

FIG. 14 illustrates still another example in which the above-mentionedexample illustrated in FIG. 8 and the above-mentioned exampleillustrated in FIG. 12 are combined. In this example, a first dustcollecting electrode 170 that has a rectangular cross section and iscontinuous in a shape of a rectangular frame, for example, is disposedso as to surround the entire periphery of the sample and so that theinner edge portion contacts with the outer edge portion of the sample200. Further, a second dust collecting electrode 172 that has arectangular cross section and is continuous in a shape of a rectangularframe, for example, is disposed at a position separated from the firstdust collecting electrode 170 by a predetermined interval so as tosurround the entire periphery of the first dust collecting electrode170. Then, the first dust collecting electrode 170 is connected to asecond power supply 174, and the second dust collecting electrode 172 isconnected to a third power supply 176.

Note that, as described above, second dust collecting electrodesextending linearly may be disposed along substantially the entire lengthof the individual sides of the first dust collecting electrode so thatthe second dust collecting electrodes surround substantially the entireperiphery of the first dust collecting electrode. Alternatively, it ispossible that the second dust collecting electrodes extending linearlyare separated from each other at a mid position.

In the example of FIG. 14, similarly to the above-mentioned example, avoltage of −1 to −5 kV, for example, is applied to the sample 200 viathe first power supply 128, and a voltage that is the same as thevoltage applied to the sample 200 is applied to the first dustcollecting electrode 170. For instance, when −3 eV is applied to thesample 200, −3 eV is applied to the first dust collecting electrode 170.Further, a voltage having the same polarity as the voltage applied tothe sample 200 and an absolute value larger than the voltage applied tothe sample 200 by 0.5 to 5 kV, for example, is applied to the seconddust collecting electrode 172. In other words, when a voltage of −3 kVis applied to the sample 200, for example, a voltage of −3.5 to −8 kV,for example, −5 kV is applied to the second dust collecting electrode172.

Also in this example, in a manner substantially similar to the exampleillustrated in FIG. 8 and the like described above, when a negativevoltage is applied to the sample 200, electric field intensity A betweenthe sample 200 and the second dust collecting electrode 172 is set to benegative (A<0). Thus, attraction force of the second dust collectingelectrode 172 is increased, and hence the probability that the seconddust collecting electrode 172 traps the dust or particles such asparticles can be increased. In addition to that, electric fieldintensity (absolute value) B between the gap control plate 124 and thesecond dust collecting electrode 172 is adjusted so that 0.1≦B (absolutevalue)≦10 kV/mm is satisfied. Thus, the probability that the second dustcollecting electrode 172 traps the dust or particles such as particlescan be further increased.

The first dust collecting electrode 170 has a thickness of, for example,0.1 to 5 mm and a width W3 of, for example, 5 to 50 mm similarly to theabove-mentioned dust collecting electrode 122 e illustrated in FIG. 11.In addition, the second dust collecting electrode 172 has a thicknessof, for example, 0.1 to 50 mm and a width W4 of, for example, 5 to 50 mmsimilarly to the above-mentioned dust collecting electrode 122illustrated in FIG. 6.

For instance, a negative voltage of −1 to −5 kV is applied to the sample200 and the first dust collecting electrode 170, and a negative voltageof −1.5 to −10 kV that is more negative than the negative voltageapplied to the sample 200 and the first dust collecting electrode 170 by−0.5 to −5 kV is applied to the second dust collecting electrode 172. Itis supposed that the gap control plate 124 has the ground potential, andthe distance Z8 between the gap control plate 124 and the second dustcollecting electrode 172 is 8 mm. Then, the electric field intensity Abetween the sample 200 and the dust collecting electrode 172 becomesnegative (A<0), and the electric field intensity (absolute value) Bbetween the gap control plate 124 and the second dust collectingelectrode 172 becomes 0.19 to 1.25 kV/mm (=1.5 to 10 kV/8 mm). Inparticular, when a voltage of −5 kV is applied to the dust collectingelectrode 122, the electric field intensity (absolute value) B becomes0.625 kV/mm (=5 kV/8 mm), which is an effective condition. In this case,the voltage is set not to exceed 10 kV/mm as a withstand voltage of thespace so that occurrence of discharge in the space can be prevented.

With reference to FIGS. 15 to 17, the prevention of adhesion of dust orparticles such as particles is described in more detail.

As illustrated in FIG. 15, if a particle made of insulation materialexists in a uniform electric field (q+=q−) between electrodesconstituted of parallel plates, the particle does not scatter though theparticle is polarized by electrostatic induction from the electricfield. However, if the electric field is a non-uniform electric field, aparticle is scattered by the charge generated by the dielectricpolarization. In addition, if a particle made of insulation materialexists in a non-uniform electric field (q+≠q−) between a pair ofelectrodes one of which is a plate as illustrated in FIG. 16, theparticle is polarized and scattered by electrostatic induction from theelectric field. If a particle made of insulation material exists in auniform electric field (q+=q−) between a pair of electrodes one of whichis a plate as illustrated in FIG. 17, the particle does not scatterthough the particle is polarized by electrostatic induction from theelectric field.

In this way, as illustrated in FIGS. 16 and 17, it is considered thatprobability that dust or particles' scatter is highly dependent oninitial charge q0 of the dust or particles such as particles beforedielectric polarization. It is considered that the initial charge q0 ofthe remaining matters is given by static electricity generated mainly byair flow when the vacuum evacuation is performed.

FIG. 18 illustrates another vacuum chamber 112 a provided to theelectro-optical inspection apparatus. Inside the vacuum chamber 112 a,there are disposed the stage 100 on which the sample 200 is placed, anda primary electro-optical system and a secondary electro-optical systemof the electro-optical inspection apparatus. The vacuum chamber 112 a isconnected two vacuum pumps 190 a and 190 b, which are connected to acommon dry pump 192. Further, inside the vacuum chamber 112 a, there isdisposed a static electricity remover 194 that ionizes gas with X-raysor UV-ray and uses the ionized gas for removing static electricity on asurface of a substance existing in the ionized gas so that dust orparticles such as particles (remaining matters) that cannot be removedby cleaning of the vacuum chamber 112 a are not electrified by thestatic electricity.

According to the example of FIG. 18, the static electricity remover 194is activated at the same time as the vacuum evacuation inside the vacuumchamber 112 a is started or before the vacuum evacuation. In addition,also during the vacuum evacuation of the inside of the vacuum chamber112 a, the static electricity remover 194 is continued to work. In otherwords, until there is no air flow in the vacuum chamber 112 a and nogeneration of static electricity by the air flow, the static electricityremover 194 is continued to work. In this way, dust or particles(remaining undesired objects) in the vacuum chamber 112 a are preventedfrom being electrified so that the initial charge q0 thereof is 0 (seeFIG. 16). Thus, probability of scattering caused by dielectricpolarization of the non-uniform electric field can be decreased.

In addition, even if the amount of the dust or particles such asparticles is small, remaining in the vacuum chamber without beingremoved by cleaning of the vacuum chamber, the dust or particles aredeposited on the upper surface of the planar structure in the vacuumchamber by action of gravity.

FIG. 19 is a perspective view illustrating an example of the planarstructure constituting the upper surface, the bottom surface, and theside surfaces on the inside of the vacuum chamber 112 illustrated inFIG. 2 or the vacuum chamber 112 a illustrated in FIG. 18, for example.FIG. 20 is a cross sectional view of FIG. 19. As illustrated in FIGS. 19and 20, the planar structure of the vacuum chamber 112 or 112 a (seeFIGS. 2 and 18), for example, is constituted of a wall body 196 having anumber of holes 196 a formed in grating on the inner surface. In thisway, because a number of holes 196 a are formed in grating on the innersurface of the wall body 196, dust or particles P such as particlesremaining in the vacuum chamber are deposited on the bottom of the holes196 a by the gravity. As illustrated in FIG. 20, the electrostaticshield effect of the grating holes 196 a prevents the electric fieldfrom entering the bottom of the grating holes 196 a. Therefore, the dustor particles (remaining matters) P deposited on the bottom of thegrating holes 196 a are not attracted by the static electricity and donot scatter. Thus, it is possible to prevent dust or particles such asparticles remaining in the vacuum chamber 112 or 112 a from adhering tothe surface of the sample 200 placed in the vacuum chamber 112 or 112 a,for example.

In the example illustrated in FIG. 19, a plurality of holes 196 a areformed on the wall body 196 in grating, namely in matrix. The number ofholes may be any number, namely, one or larger, and a size of the holeshould be set so that the particles or the like deposited in the holeare not scattered by the electrostatic shield effect. In addition, whena plurality of holes are formed, any arrangement can be adopted insteadof the grating arrangement.

FIG. 21 is a perspective view illustrating another example of the wallconstituting the planar structure of the vacuum chamber 112 illustratedin FIG. 1 or the vacuum chamber 112 a illustrated in FIG. 18. FIG. 22 isa cross sectional view of FIG. 21. As illustrated in FIGS. 21 and 22,the planar structure of the vacuum chamber 112 or 112 a (FIGS. 2 and 18)is constituted of a plate-like wall body 198 and a plate 199 having amesh structure disposed in parallel to the wall body 198 with apredetermined interval between them. The plate 199 having a meshstructure is constituted of a mesh-like or net-like metal plate and isconnected to an independent power supply 102.

In the example illustrated in FIGS. 21 and 22, dust or particles Premaining in the vacuum chamber 112 or 112 a are allowed to pass throughthe plate 199 having a mesh structure and reach the surface of the wallbody 198 by the gravity. The wall body 198 is covered with the plate 199having the mesh structure, and hence the electric field is blocked bythe plate 199 having a mesh structure and does not reach the surface ofthe wall body 198. Therefore, the dust or particles (remaining matters)P reaching the surface of the wall body 198 are not attracted by thestatic electricity and are not scattered. Thus, it is possible toprevent dust or particles remaining in the vacuum chamber 112 or 112 afrom adhering to the surface of the sample placed in the vacuum chamber112 or 112 a, for example.

In particular, by applying the voltage independently to the plate 199having the mesh structure, dust or particles P remaining in the vacuumchamber can be positively attracted by the plate 199 having the meshstructure, and together with gravity action of the dust or particles P,the dust or particles P can be deposited and fixed to the surface of thewall body 198 constituting the planar structure of the vacuum chamber112 or 112 a, for example.

Next, there is described a structure for enabling to image the samplesurface with high contrast in the case where the insulation region andthe conductive region are formed on the surface of the sample 200according to the present invention.

FIGS. 23A and 23B are diagrams illustrating an example of a relationshipbetween landing energy of the electron beam for imaging and materialcontrast in the obtained image when the image is obtained using themapping projection type electro-optical inspection apparatus illustratedin FIG. 1. The material contrast means contrast due to a differencebetween electrons generated from the conductive material and electronsgenerated from the insulation material. FIG. 23A is a diagramillustrating an example of the image obtained depending on the landingenergy band, and FIG. 23B is a graph illustrating correlation betweenthe landing energy of the electron beam for imaging and detectorcurrent.

In FIG. 23B, the horizontal axis represents landing energy (LE) of theelectron beam for imaging, and the vertical axis represents a value ofthe detector current of the detector 400. In addition, in FIG. 23B, thesolid line is a characteristic curve in a case where the NA adjustmentaperture plate 360 having an aperture diameter of 10 to 300 μm is used.The dot-dashed line is characteristic curve in a case where the NAadjustment aperture plate 360 having an aperture diameter of 1,000 to3,000 μm is used. In the example illustrated in this diagram, thelanding energy (LE) of 2 to 10 eV is a “secondary electron region”, thesame of −2 to 2 eV is the “transition region”, and the same of −2 eV orlower is the “mirror electron region”.

The term “secondary electron” means an electron emitted from the sample200 when the electron beam collides with the surface of the sample 200.The secondary electrons may include reflection electrons havingreflection energy that is substantially the same as incident energy andbackward scattering electrons that scatter backward in addition to theso-called secondary electrons, as long as the electrons are emitted fromthe sample 200 when the electron beam collides with the sample surface.Electrons that are mainly detected in the “secondary electron region”are secondary electrons that are emitted from the sample 200 in a manneraccording to the cosine rule.

In addition, the “mirror electron” means an electron that is reflectionof the electron beam that is irradiated toward the surface of the sample200 and does not collide with the sample surface but changes thepropagation direction oppositely in the vicinity of the sample surface.For instance, if the sample surface has a negative potential and landingenergy of the electron beam is small, there is a phenomenon that theelectron beam does not collide with the sample surface but changes thepropagation direction oppositely due to the electric field near thesample surface. In the sample observation apparatus and the sampleobservation method according to the present invention, such electronsthat do not collide with the sample surface but change the propagationdirection oppositely as reflection are referred to as mirror electrons.

In FIG. 23B, in the secondary electron region having a landing energy(LE) of 2 to 10 eV, detection current is greatly different due to adifference of aperture diameter of the NA adjustment aperture plate 360.This is because a sample surface emission angle of the secondaryelectron is expressed by the cosine rule, and hence spread of electronsat a position of the NA adjusting aperture 360 is large.

Then, as the landing energy (LE) is decreased to 2 eV or lower, themirror electrons increase gradually to be the “transition region” inwhich the mirror electrons and secondary electrons are mixed. Asillustrated in FIG. 23B, a detector current difference due to thedifference of aperture diameter of the NA adjustment aperture plate 360is small.

In addition, when the landing energy (LE) becomes −2 eV or lower, themirror electron region appears in which emission of the secondaryelectrons does not occur and emission amount of the mirror electrons isconstant. In this region, the detector current does not depend on anaperture diameter of the NA adjustment aperture plate 360. Therefore, itcan be considered that the mirror electrons are concentrated in a rangeof φ300 μm or smaller and φ10 μm or larger at the position of the NAadjustment aperture plate 360. This is because the mirror electron doesnot collide with the sample surface but is reflected, and therefore hasgood directivity and high straightness.

Note that, in the example illustrated in FIG. 23B, the characteristiccurve is considered to be the same as illustrated in the solid line inthe case where the aperture diameter is smaller than 10 μm and to be thesame as illustrated in the broken line in the case where the aperturediameter is larger than 3,000 μm. However, it is supposed here that theaperture diameter is 10 μm or larger and 3,000 μm or smaller because ofa limit of measurement due to increasing noise.

FIG. 24 is a diagram schematically illustrating a difference of anglebetween the mirror electron having structural information of the samplesurface and the secondary electron, in which the horizontal axisrepresents the effective landing energy (LE). In FIG. 24, a relationshipbetween the effective landing energy and behavior of the electron isillustrated for each of the mirror electron region and the transitionregion.

FIG. 24 illustrates an example in which a region having effectivelanding energy (LE) smaller than 0 eV becomes the mirror electronregion. As illustrated in this diagram, the mirror electron is generatedwhen the irradiation electron beam does not collide with the samplesurface but is reflected to the front of the sample surface. In thiscase, if the irradiation beam enters the sample surface perpendicularly,the mirror electron is reflected perpendicularly to the sample surface.As a result, propagation direction of the mirror electron is constant.

In contrast, in the transition region, some of the irradiation electronbeams do not collide with the sample surface but are reflected to thefront of the sample surface to be mirror electrons, and others of theirradiation electron beams collide with the sample surface so that thesecondary electrons are emitted from the inside to the outside of thesample. Here, in the same manner as in the mirror electron region, ifthe irradiation beam enters the sample surface perpendicularly, themirror electron is reflected perpendicularly to the sample surface sothat the propagation direction of the mirror electron is constant. Onthe other hand, the secondary electrons are emitted in variousdirections so that the emission amount is proportional to cosine of anangle between the normal of the sample surface and the emissiondirection (observation direction), namely according to the so-called“cosine rule”. Then, a ratio of the secondary electrons to the mirrorelectrons becomes higher as the landing energy becomes higher (towardthe right side in FIG. 24).

In other words, as illustrated in FIG. 24, the mirror electrons have aconstant propagation direction and good directivity, but the secondaryelectrons propagate in various directions according to the cosine ruleso that the directivity is not high.

In the above-mentioned example, the range of landing energy from −2 eVto 2 eV corresponds to the transition region, namely the region wherethe mirror electrons and the secondary electrons are mixed. However,this landing energy range can change depending on the sample to beobserved. The inventors of the present invention have found from variousexperiments that use of the irradiation electron beam having landingenergy in the transition region is effective for high contrastobservation of a sample surface pattern, in particular, high contrastobservation of a sample surface on which an insulation region and aconductive region are formed.

According to study by the inventors of the present invention, it isfound that when the lowest landing energy of the transition region isdenoted by LEA while the highest landing energy is denoted by LEB, it ispreferred to set the primary landing energy (LE) of the electron beamfor imaging to a value that satisfies LEA≦LE≦LEB or LEA≦LE≦LEB+5 eV.Hereinafter, this is described in detail.

FIG. 25 is a diagram illustrating a variation of the gradation of thesample surface with respect to the landing energy (LE). The gradation isproportional to the number of electrons obtained by the detector 400. Asillustrated in FIG. 25, the region where the landing energy (LE) is LEAor lower is the mirror electron region, the region where the landingenergy (LE) is LEB or higher is the secondary electron region, and theregion where the landing energy (LE) is LEA or higher and LEB or loweris the transition region.

According to various experiments carried out by the inventors of thepresent invention, it is confirmed that the range in which LEA to LEB is−5 eV to +5 eV is a preferred range in many cases.

Further, a gradation difference occurs due to a difference of formingstate of mirror electrons between the insulation region and theconductive region. As the gradation difference is larger, highercontrast is formed. In other words, a difference of material orstructure causes a difference of forming state of mirror electrons sothat the gradation difference is formed. In order to generate highcontrast between the insulation region and the conductive region in theobtained image, it is very important how the above-mentioned landingenergy (LE) is set. Specifically, it is very effective for obtaininghigh contrast to use the landing energy (LE) in the region satisfyingLEA≦LE≦LEB (for example, −5 eV to +5 eV) or the region satisfyingLEA≦LE≦LEB+5 eV (for example, −5 eV to +10 eV (=(5+5)eV)).

With reference to FIGS. 23A and 23B again, contrast between theinsulation material and the conductive material in each generatedelectron region is described. It should be noted that, various materialsmade of conductor or insulator can be used for the conductive materialand the insulation material. For instance, tungsten (W) can be used forthe conductive material, and silicon oxide (SiO₂) film can be used forthe insulation material.

FIG. 23A illustrates an example of material contrast in the imageobtained by the irradiation electron beam having the landing energy (LE)of each generated electron region. FIG. 23A illustrates an example ofmaterial contrast in the secondary electron region, the transitionregion and the mirror electron region. First, noting the materialcontrast in the mirror electron region, there is no difference ofluminance between the conductive material and the insulation material sothat the material contrast is not obtained. This is because everyirradiation electron is reflected before the sample surface in themirror electron region, and therefore there is no difference ofluminance, namely no difference of the number of electrons between theconductive material and the insulation material.

In addition, there is a luminance difference between the conductivematerial and the insulation material in each of the transition regionand the secondary electron region. The transition region has a higherluminance difference between the conductive material and the insulationmaterial, and as a result, has a higher material contrast. The reason isconsidered to be that not only the secondary electrons but also mirrorelectrons having high directivity are detected in the transition region,and therefore the signal amount is increased so that the luminance isenhanced.

In this way, if a sample surface image is obtained in the transitionregion in which the secondary electrons and the mirror electrons aremixed, material contrast between the conductive material and theinsulation material can be enhanced.

When the electron beam irradiates the sample surface in the transitionregion in advance before imaging, the potential of the conductivematerial remains to be the ground potential while the insulationmaterial is electrified so that the potential is changed by a few eVnegatively. As a result, energy (speed) of electron is different betweenthe electron having structural information of the conductive materialand the electron having structural information of the insulationmaterial.

Further, when the electrons having different speeds pass through the E×Bdeflector 340 (see FIG. 1), an orbit shift occurs according to the speeddue to the following reason.

The E×B deflector 340 is a means for generating an electric field E anda magnetic field B. An electron passing through the E×B 340 receives aforce FE=e·E from the electric field and a force FB=e·(v×B) from themagnetic field. Here, e is the charge of electron that is 1.602×10⁻¹⁹C,and E and B are the electric field (V/m) and the magnetic field (Wb/m²),respectively.

In these forces, the force FE=e·E due to the electric field does notdepend on the electron speed v (m/s), but the force FB=e·(v×B) due tothe magnetic field depends on the electron speed v (m/s).

Usually, a condition (Wien condition) is set for the electron emittedfrom the conductive substrate, namely the sample, to propagate straightthrough the E×B deflector 340. However, because of the above-mentionedreason, when the electron speed v (m/s) changes, the force affected byaction of the magnetic field changes, and hence the orbit of theelectron after passing through the E×B deflector 340 is shifted.

In other words, as described above, the E×B deflector 340 is a means fordirecting the orbit of the electron having structural information of thesample surface when the electron beam irradiates according to the speedof the electron beam propagating in the direction opposite to theincident direction. Further, utilizing the above-mentioned shift of theelectron orbit, it is possible to guide selectively the electrons havingstructural information of the conductive region or the electrons havingstructural information of the insulation region to pass through the NAaperture 361 and to reach the detector 400.

Note that, the transition region is the energy region in which thesecondary electrons and the mirror electrons are mixed. Therefore, inthis energy region, electron orbits of the secondary electron and themirror electron from the insulation region are both shifted.

FIGS. 26A and 26B are schematic diagrams illustrating an example oforbit of the electron having structural information of the surface ofthe sample 200. FIG. 26A is a side view of the electron orbit, and FIG.26B is a partially enlarged diagram of the electron orbit viewed fromthe underside of the movable NA aperture.

In FIG. 26A, a negative potential is applied to the sample 200 from thepower supply 128 for the sample. The sample 200 includes conductivematerial 202 and insulation material 203 covering the conductivematerial 202. The conductive material 202 is exposed at a hole 204 as abreak in the insulation material 203. For instance, a reticle usuallyhas a contact structure in which the bottom of the hole 204 isconstituted of the conductive material 202 like the sample 200illustrated in FIG. 26A. Note that, for simplification, only the E×Breflector 340, the NA adjustment aperture plate 360, and the detector400 are illustrated as elements of the electro-optical inspectionapparatus.

In FIG. 26A, an electron beam EB is emitted from the upper right and isdeflected by the E×B deflector 340 so as to enter the sample 200perpendicularly. Then, among electrons having structural information ofthe sample surface, the electrons ec having structural information ofthe conductive region 202 propagate straight and passes through the NAaperture 361 of the NA adjustment aperture plate 360. On the other hand,the electrons ei having structural information of the insulation region203 are shifted in orbit by action of the E×B deflector 340 and collidewith the NA adjustment aperture plate 360 around the NA aperture 361 soas not to pass through the NA aperture 361. As a result, the electronsec having structural information of the conductive region 202 reach thedetector 400, while the electrons ei having structural information ofthe insulation region 203 do not reach the detector 400.

A reticle usually has a contact structure in which most part of thesurface of the sample 200 is occupied by the insulation material 203,and a part (the bottom of the hole 204) includes the conductive material202. In this structure, only the electrons ec having surface structuralinformation of the conductive material 202 are guided to the detector400 while the electrons ei having surface structural information of theinsulation material 203 are not allowed to reach the detector 400. Thus,an image with very high contrast can be obtained.

To the contrary, only the electrons ei having surface structuralinformation of the insulation material 203 are guided to the detector400 while the electrons ec having surface structural information of theconductive material 202 are not allowed to reach the detector 400. Thus,an image with very high contrast can be obtained.

This method of reverse of contrast is effective in particular fordetecting a short defect and an open defect existing in a pattern inwhich areas of the conductive material and the insulation material aresubstantially the same on the sample surface. If an area of one of theconductive material and the insulation material is conspicuously smallerthan an area of the other material in the pattern, material regionshaving the conspicuously small area are dotted in the material region ofthe large area. The electrons from the material region of the large areaare slightly diverged in a light path to a detector. Because of thisdiverging action, an image obtained by the electrons from the materialregion having small area is smaller than an original image, and hencethe defect detection becomes difficult. For instance, in a structure(contact plug structure) in which conductive regions having a contactplug shape of conspicuously small area are dotted in the largeinsulation region formed on a silicon substrate, an image formed by theelectrons from the conductive region has an area smaller than theoriginal area because of diffusion (diffraction) of electrons from theinsulation region.

It is supposed that the electrons ec and ei include both the mirrorelectrons and the secondary electrons. In addition, separation anddetection of the generated electrons according to a type of material canbe applied not only to a reticle but also to a line/space pattern of asemiconductor wafer or the like in the same manner.

FIG. 26B is an enlarged diagram illustrating a relationship among the NAaperture 361, the electrons ec having surface structural information ofthe conductive material 202, and the electrons ei having surfacestructural information of the insulation material 203 viewed from theunderside of the NA adjustment aperture plate 360.

In the example illustrated in FIG. 26B, a position of the NA aperture361, which is formed in a part of the rectangular NA adjustment apertureplate 360, is adjusted so that the electrons ec having structuralinformation of the conductive region 202 pass through the NA aperture361, while most of the electrons ei having structural information of theinsulation region 203 are blocked by the NA adjustment aperture plate360 and cannot pass through the NA aperture 361.

As to the mirror electrons, electron orbits of the conductive material202 and the insulation material 203 cross over at the position of the NAadjusting aperture plate 360, and form a minimum spot of 100 μm.Therefore, it is easy to separate the electrons ec having structuralinformation of the conductive material 202 selectively without losingoptical resolution by the NA adjustment aperture plate 360 by utilizingthe orbit shift by the E×B deflector 340.

As the above-mentioned potential difference between the conductivematerial and the insulation material due to electrification is larger,positional movement in the position of the NA adjustment aperture plate360 is also larger. Therefore, when the electrified potential differenceis increased, even if the NA aperture 361 having a large aperturediameter is used, it is possible to separate the electrons ec havingstructural information of the conductive region 202 from the electronsei having structural information of the insulation region 203. Then, byusing the NA aperture 361 having a large aperture diameter, it ispossible to increase the number of detected electrons for forming animage.

Note that, when the charged electron beam is to irradiate the insulationregion 203 of the sample 200 before the electron beam for imagingirradiates, the charged electron beam only has to irradiate the surfaceof the sample 200 without performing imaging by the detector 400, whileusing the electron beam source 310 illustrated in FIG. 1 or the chargedelectron beam irradiation means 700, if disposed. In this case, it ispossible to irradiate only the insulation region 203 with the chargedelectron beam, but the surface potential of the conductive region 202 is0 even if it is irradiated with the charged electron beam. Therefore,without any distinction, the imaging region of the sample 200 may beirradiated with the charged electron beam having predetermined landingenergy.

FIGS. 27A and 27B are diagrams illustrating an optimal position of theNA aperture 361 for obtaining high material contrast in the case of themirror electrons and in the case of the secondary electrons. FIG. 27A isa diagram illustrating an optimal position of the NA aperture 361 of theNA adjustment aperture plate 360 in the case of the mirror electrons.FIG. 27B is a diagram illustrating an optimal position of the NAaperture in the case of the secondary electrons. In addition, in FIGS.27A and 27B, a circle filled with black color indicates the electrons echaving structural information of the conductive region 202, and a circlefilled with gray color indicates the electrons ei having structuralinformation of the insulation region 203. As illustrated in thesefigures, the optimal position of the NA aperture 361 at the position ofthe NA adjustment aperture plate 360 is different depending on adifference of spread of the orbit of the mirror electrons or thesecondary electrons.

In FIG. 27B, at the position of the NA adjustment aperture plate 360, adifference of electron orbit shift between the secondary electrons echaving structural information of the conductive region 202 and thesecondary electrons ei having structural information of the insulationregion 203 is approximately 100 μm, and the electron distributions areoverlapped with each other in most part. This is because that thesecondary electrons propagate in various directions according to thecosine rule so that the directivity is not high, as described above.Therefore, it is considered to be optimal to adjust the center of the NAaperture 361 of the NA adjustment aperture plate 360 to a positionsubstantially identical to the center of the orbit of the electrons ecemitted from the conductive region 202, in order to increase thematerial contrast by the secondary electrons. When the center of the NAaperture 361 is adjusted to the position, the electrons ec can bedetected with reference to the center of the part having the highestelectron density of the electrons ec emitted from the conductive region202 of the sample 200.

However, as illustrated in FIG. 27B, the electron orbit of the electronsei emitted from the insulation region 203 substantially overlaps withthe orbit of the electrons ec emitted from the conductive region 202,and hence the electrons cannot be detected separately. Therefore, in thesecondary electron emission region, the material contrast isdistinguished between the secondary electrons ec emitted from theconductive region 202 and the secondary electrons ei emitted from theinsulation region 203, based on a signal difference thereof.

In contrast to the above, in FIG. 27A, there is a conspicuous differenceof the electron orbit shift between the mirror electrons ec havingstructural information of the conductive region 202 and the mirrorelectrons ei having structural information of the insulation region 203.In the example illustrated in FIG. 27A, at the position of the NAadjustment aperture plate 360, a difference of electron orbit shiftbetween the mirror electrons ec having structural information of theconductive region 202 and the mirror electrons ei having structuralinformation of the insulation region 203 is approximately 100 μm. Theelectron distributions are not overlapped with each other in most partbut are substantially separated. This is because the mirror electron hasa constant propagation direction and good directivity as describedabove.

In this case, for example, it is easy to set an arrangement in which allthe electrons ec having structural information of the conductive region202 pass through the NA aperture 361 while the electrons ei havingstructural information of the insulation region 203 hardly pass throughthe NA aperture 361. Then, if the position adjustment of the NA aperture361 is performed in such a manner, the electrons ec having structuralinformation of the conductive region can be separated from the electronsei having structural information of the insulation region, and many ofonly the electrons ec having structural information of the conductiveregion can be guided to the detector 400. As a result, material contrastbetween the conductive region 202 and the insulation region 203 can beenhanced. In other words, by using the mirror electrons generated in thetransition region, the electrons ec having structural information of theconductive region can be separated from the electrons ei havingstructural information of the insulation region 203. As a result, itbecomes easy to obtain an image with high material contrast.

Usually, in order to perform such separation, a chromatic aberrationcorrector (monochrometer) is necessary which is constituted of aplurality of magnetic fields and electric fields. According to theelectro-optical inspection apparatus and the sample observation methodof the present invention, an image with high material contrast can beobtained only by position adjustment of the NA aperture 361 formed inthe NA adjustment aperture plate 360 without disposing a chromaticaberration corrector.

Note that, FIGS. 26A and 26B and 27A and 27B illustrate the case wherethe electrons ec having structural information of the conductive region202 are selectively guided to the detector 400 and the electrons eihaving structural information of the insulation region 203 are notguided to the detector 400. However, it is possible to adopt a structurein which the electrons ei having structural information of theinsulation region 203 are selectively guided to the detector 400 and theelectrons ec having structural information of the conductive region 202are not guided to the detector 400, by setting of the E×B deflector 340,layout of the NA adjustment aperture plate 360, and adjustment ofdiameter of the aperture 361.

It should be set as appropriate according to the use whether theelectrons ec having structural information of the conductive region 202or the electrons ei having structural information of the insulationregion 203 are selectively guided to the detector 400 to be detected.

As described above, the electro-optical inspection apparatus accordingto the present invention includes the electron beam source forirradiating the sample surface having the insulation region and theconductive region with the electron beam for imaging, theelectromagnetic field generation means (E×B deflector) for directing, byan electric field and a magnetic field, the electrons having structuralinformation of the sample surface by the irradiation with the electronbeam for imaging, according to speed of the electrons propagating in thedirection opposite to the incident direction of the electron beam forimaging, the detector for detecting the electrons directed by theelectromagnetic field generation means (E×B) so as to obtain the samplesurface image from the detected electrons, the landing energy settingmeans for setting the landing energy of the electron beam for imaging tothe transition region in which the electrons include both the mirrorelectrons and the secondary electrons, the NA aperture moving mechanismfor enabling adjustment of the NA aperture position defining thenumerical aperture (NA) in the plane, and the charged electron beamirradiation means for irradiating the sample surface with the electronbeam so as to electrify the insulation region. Then, through theposition adjustment of the NA aperture by the NA aperture movingmechanism, the electrons having structural information of the conductiveregion and the electrons having structural information of the insulationregion, which are directed differently by action of the E×B deflector,can be selectively guided to the detector.

In addition, the image processing device 500 is provided with acalculation function (calculation part), which determines whether or nota short defect exists from the image obtained from the electron havingstructural information of the conductive region, and determines whetheror not an open defect exists from the image obtained from the electronhaving structural information of the insulation region. Thus, theelectro-optical inspection apparatus can be used as a detectionapparatus for a short defect and an open defect.

Further, the sample observation method of the present invention can beperformed by using the electro-optical inspection apparatus having theabove-mentioned structure. In the method, an image is obtained under thecondition where the luminance of the conductive region is higher thanthe luminance of the insulation region, and another image is obtainedunder the condition where the luminance of the insulation region ishigher than the luminance of the conductive region. Thus, the samplesurface on which the insulation region and the conductive region areformed can be observed with high contrast, and detection of a shortdefect or an open defect, as well as classification of a type of thedefect can be performed easily. Hereinafter, the sample observationmethod of the present invention is described.

In the sample observation method of the present invention, in the samplesurface having the insulation region and the conductive region, thelanding energy (LE) of the imaging electron beam is adjusted to thetransition region in which the electrons having structural informationof the sample surface include both the mirror electrons and thesecondary electrons, and an image is obtained under the condition wherethe luminance of the conductive region is higher than the luminance ofthe insulation region while another image is obtained under thecondition where the luminance of the insulation region is higher thanthe luminance of the conductive region. In other words, in the sampleobservation method of the present invention, an image is obtained underthe condition of a relationship where contrast is reversed between theconductive region and the insulation region.

As described above, by using the mirror electrons generated in thetransition region, the electrons ec having structural information of theconductive region can be separated from the electrons ei havingstructural information of the insulation region 203. As a result, itbecomes easy to obtain an image with high contrast. The sampleobservation method of the present invention utilizes this principle. Inorder to easily understand the feature of the method, the results of abasic study about formation of contrast between the conductive regionand the insulation region are described in advance.

FIG. 28A is a diagram illustrating a structure of the sample 200described above in relation to FIG. 26A and illustrates a crosssectional structure of the sample 200 having a plurality of contactplugs. FIG. 28B is a diagram illustrating an example of the obtainedimage of the surface of the sample 200 having the contact plugstructure.

In FIG. 28A, the insulation region 203 and the conductive region 202 areformed on a silicon substrate 205 that is a semiconductor substrate. Theinsulation region 203 is made of SiO₂. In addition, the conductiveregion 202 is made of material of tungsten (W) to form a contact plugshape. On the sample surface, there are formed a plurality of conductiveregions 202 in dots or circles in the insulation region 203 as a base.

FIG. 28B is a diagram illustrating an example of the image of the samplesurface 201 obtained by sample observation. This image is obtained underthe condition where the luminance of the conductive region is higherthan the luminance of the insulation region in which the position of theNA aperture 361 of the NA adjustment aperture plate 360 is adjusted sothat the electrons generated from the conductive region 202 areselectively detected. As a result, the black insulation region 203occupies the base of the image, from which the white circular conductiveregions 202 come to the surface, as a high contrast image.

In this way, by separating the electrons ec having structuralinformation of the conductive region from the electrons ei havingstructural information of the insulation region 203, the contrast can beenhanced. As a result, it is possible to obtain an image in which theinsulation region 203 can be easily distinguished from the conductiveregion 202, and hence observation or inspection of a defect or the likecan be also performed easily.

On the contrary, if the position of the NA aperture 361 of the NAadjustment aperture plate 360 is adjusted so that the electronsgenerated from the insulation region 203 are selectively detected, animage is obtained under the condition where the luminance of theinsulation region is higher than the luminance of the conductive region.Therefore, on the contrary to FIG. 28B, an image is obtained in whichthe insulation region 203 becomes white with high luminance, and theconductive region 202 becomes black with low luminance.

Next, an example of setting a condition for obtaining an image with highcontrast is described.

FIGS. 29A and 29B are diagrams illustrating, by means of an example,results of studying the landing energy (LE) condition for obtaining animage with high contrast. In this example, a cathode voltage of theelectron source 311 of the electron beam source 310 was set to −3,995 to−4,005 eV, and a voltage of the surface of the sample 200 was set to−4,000 eV. In addition, the transition region was optimized by settingthe landing energy (LE) to −1 eV. Irradiation current density of theelectron beam was set to 0.1 mA/cm², and a pixel size of the detector400 was set to 50 nm/pix. An aperture diameter of the NA aperture 361 ofthe NA adjustment aperture plate 360 was set to φ150 μm, and predose bythe charged electron beam was set to 1 mC/cm².

FIG. 29A is a table showing results of measuring the contrast under theabove-mentioned condition, in which the landing energy (LE) of theelectron beam was changed to observe the contact plug having the crosssectional structure illustrated in FIG. 28A. FIG. 29B is a graph of theresults of measurement shown in FIG. 29A.

In the graph illustrated in FIG. 29B, the horizontal axis represents thelanding energy (LE), and the vertical axis represents the averagegradation of the obtained image. The characteristic curve of theinsulation region is illustrated as a curve connectingsubstantially-square symbols, and the characteristic curve of theconductive region is illustrated as a curve connecting rhombus symbols.In addition, results of calculating contrast from the average gradationof the insulation region and the conductive region are illustrated as acurve connecting triangle symbols. Note that, the contrast wascalculated using Expression (1) described below.

Contrast=|(Average Gradation of Conductive Material)−(Average Gradationof Insulation Material)|/((Average Gradation of ConductiveMaterial)+(Average Gradation of Insulation Material))  (1)

In FIGS. 29A and 29B, when the landing energy (LE) is −1 eV, thecontrast is 0.8 as a highest value. The landing energy (LE) of −1 eV isin the transition region in which the mirror electron and the secondaryelectron are mixed as the electrons from the sample 200 as describedabove in relation to FIGS. 23A and 23B. In addition, as illustrated inFIGS. 23A and 23B, −5 eV is the landing energy (LE) of the mirrorelectron region, and 5 eV is the landing energy (LE) of the secondaryelectron region, in either of which regions the contrast is low.

It is understood that highest contrast is obtained when the landingenergy (LE) is in the transition region.

FIGS. 30A and 30B are diagrams illustrating a correlation between doseand contrast of the charged electron beam obtained by a production testusing the sample 200 illustrated in FIG. 28A. FIG. 30A is a tableshowing results of measuring the correlation between dose and contrastof the charged electron beam, and FIG. 30B is a graph of the results ofmeasurement illustrated in FIG. 30A. Note that, various settingconditions of the electro-optical inspection apparatus and the sample tobe measured are as described above, and description thereof is omitted.In addition, the contrast was calculated by Expression (1) describedabove from the average gradation of the insulation region and theconductive region in the image obtained by imaging the sample surfaceafter irradiating the sample surface with the charged electron beam.

As illustrated in FIGS. 30A and 30B, as dose of the charged electronbeam becomes higher, the contrast becomes higher, but the contrast issaturated at a certain dose. In the example illustrated in FIGS. 30A and30B, the contrast remains to be 0.8 even if the sample surface beforeimaging is irradiated with the charged electron beam of 1 mC/cm² orhigher in advance. In other words, when the dose of the charged electronbeam is 1 mC/cm² or higher, the contrast is saturated. This means thatwhen the dose of the charged electron beam is 1 mC/cm² or higher,electrification of the insulation region 203 of the sample surface issaturated to be a negative potential so that stable contrast can beobtained.

FIGS. 31A and 31B are diagrams supplementarily illustrating that highcontrast can be obtained by separating the electrons ec havingstructural information of the conductive region from the electrons eihaving structural information of the insulation region 203, and arediagrams illustrating values obtained by a production test using thesample 200 illustrated in FIG. 28A (however, Cu was used instead of W asthe conductive material). FIG. 31A is a table showing dependence on thelanding energy (LE) of the secondary electron emission efficiency andthe contrast of materials of the conductive region (Cu) and theinsulation region (SiO₂), in the case where the electrons ec havingstructural information of the conductive region are not separated fromthe electrons ei having structural information of the insulation region.In addition, FIG. 31B is a graph of this table.

When the electrons ec having structural information of the conductiveregion are not separated from the electrons ei having structuralinformation of the insulation region, the obtained contrast depends ononly the luminance difference corresponding to emission efficiency ofthe secondary electrons of each material. In other words, the positionadjustment of the NA aperture 361 cannot obtain contrast occurring inthe image obtained by enhancing electrons having structural informationof either region.

According to the results illustrated in FIGS. 31A and 31B, when theelectrons ec having structural information of the conductive region arenot separated from the electrons ei having structural information of theinsulation region, the obtained contrast is approximately 0.4 at most,which is conspicuously lower than the contrast (for example, 0.8 asdescribed above) obtained when the electrons ec having structuralinformation of the conductive region are separated from the electrons eihaving structural information of the insulation region.

In other words, as in the present invention, by utilizing the mirrorelectrons generated in the transition region, the electrons ec havingstructural information of the conductive region are separated from theelectrons ei having structural information of the insulation region, andthen an image is obtained under the condition where the luminance of theconductive region is higher than the luminance of the insulation region,or an image is obtained under the opposite condition where the luminanceof the insulation region is higher than the luminance of the conductiveregion. Thus, conspicuously higher contrast can be obtained than theimage obtained by sample observation without separating the electrons echaving structural information of the conductive region from theelectrons ei having structural information of the insulation region.

FIG. 32A is a diagram showing the contrast when the ratio of area(pattern width) between the conductive region 202 and the insulationregion 203 of the surface of the sample 200 illustrated in FIG. 28A ischanged, in comparison between results of measurement using the mappingprojection type low acceleration electron beam apparatus as a low-energyelectron microscopy (LEEM) type and results of measurement by aproduction test using the SEM type. FIG. 32B is a graph of the resultsof measurement shown in FIG. 32A. Note that, the results of measurementillustrated here are based on the image obtained under the conditionwhere the luminance of the conductive region is higher than theluminance of the insulation region, and are obtained under theabove-mentioned various setting conditions, and description thereof isomitted.

According to the LEEM type electro-optical inspection apparatus andsample observation method, mainly the conductive region 202 has highluminance as illustrated in FIG. 27B. Therefore, if the ratio of area ofthe conductive region 202 is decreased, the contrast increases becauseof little interference from the surroundings. On the other hand, in theSEM type (for example, the landing energy is approximately 1,000 eV),the insulation material 203 is brighter by the secondary electronemission coefficient of the material. If the ratio increases, a signalof the conductive region 202 is eliminated by spread of the orbit of thesecondary electron, and hence the contrast becomes very low.

As illustrated in FIGS. 32A and 32B, when the ratio of area between theconductive region 202 and the insulation region 203 is small, adifference of contrast is relatively small. When the ratio of areabetween the conductive region and the insulation region is 1:2, thedifference of contrast is controlled to be approximately 0.3. However,as the area of the insulation region 203 in the sample surfaceincreases, contrast of the LEEM type is increased, but contrast of theconventional SEM type is decreased. When the ratio of area between theconductive region and the insulation region is 1:10, the difference ofcontrast reaches 0.75.

In this way, the LEEM type sample observation is effective particularlyfor observation of the sample 200 having a low ratio of the conductivematerial 202. In other words, for observation of the contact structurein which a ratio of the insulation material 203 in the sample surface islarge, an image with high contrast can be obtained, and hence a largeadvantage can be obtained. In addition, on the contrary, when an imageis obtained under the condition where the luminance of the insulationregion is higher than the luminance of the conductive region,observation can be performed effectively also for the sample 200 havinga low ratio of the insulation material 203 and a high ratio of theconductive material 202 in the sample surface.

FIG. 33 is a schematic diagram illustrating a second embodiment of theelectro-optical inspection apparatus according to the present invention.The second embodiment has the same basic structure as the embodimentillustrated in FIG. 1. In other words, the electro-optical inspectionapparatus illustrated in FIG. 33 is the mapping projection typeelectro-optical inspection apparatus, which includes the electron beamsource 310, the primary lens 320, the condenser lens 330, the E×Bdeflector 340, the transfer lens 350, an NA adjustment aperture plate360 a, the projection lens 370, the detector 400, the image processingdevice 500, the stage 100, and the energy adjust/supply unit 600 in thesame manner as the structure illustrated in FIG. 1. In theelectro-optical inspection apparatus illustrated in FIG. 33, the samecomponent as in the electro-optical inspection apparatus illustrated inFIG. 1 is denoted by the same numeral or symbol, and description thereofis omitted.

Although not illustrated in FIG. 33, the electro-optical inspectionapparatus of the second embodiment may also include the charged electronbeam irradiation means 700 (see FIG. 1) as necessary.

The electro-optical inspection apparatus illustrated in FIG. 33 isdifferent in structure from the electro-optical inspection apparatusillustrated in FIG. 1 in that the NA adjustment aperture plate 360 aincludes a movable, multi-selectable NA adjusting aperture movingmechanism. In other words, the NA adjustment aperture plate 360 aincludes a plurality of types of NA apertures 361 and 362 havingdifferent aperture diameters, and the NA apertures 361 and 362determining the numerical aperture (NA) can be adjusted in position (canbe switched) in the plane by the NA aperture moving mechanism (notshown).

In the electro-optical inspection apparatus illustrated in FIG. 33, theNA adjustment aperture plate 360 a has a plurality of NA apertures 361and 362 having different sizes, and is moved in the horizontal directionso that the NA aperture 361 and the NA aperture 362 can be switched.Thus, because a desired numerical aperture (NA) can be set, an NAaperture of an optimal numerical aperture (NA) can be selected accordingto the type of the sample 200, the structure of the sample surface, orother various conditions so that a sample surface image with highmaterial contrast can be obtained.

As described above, because the NA moving mechanism is disposed, signalsfrom the sample surface can be selected effectively so that highcontrast can be obtained. In this case, it is further effective to addthe content and structure described above with reference to FIGS. 2 to14. It is necessary to eliminate or reduce as much as possible dust orparticles generated by the apparatus itself in ultrafine patterninspection or foreign matter inspection according to the presentinvention. It is because that the inspection using this apparatus isusually performed after cleaning or before exposure of the sample, andif dust or particles adhere in this case, the dust or particles causeincrease of defects in the exposure process or increase of defects in aprocess after the cleaning Therefore, using the method and apparatusdescribed above with reference to FIGS. 2 to 14, the adhesion of thedust or particles can be prevented as much as possible so thatreliability of the apparatus can be maintained. In addition, if theapparatus includes the SEM mounted on the same chamber as illustrated inFIG. 2, the generated dust or particles can be confirmed promptly afterthe inspection. Therefore, efficiency of the process can be improvedeffectively. In addition, there is an effect of preventing adhesion ofdust or particles that may be caused when a sample is put in anotherindependent review apparatus.

FIGS. 34A and 34B are diagrams illustrating an example of a structure ofthe above-mentioned movable type NA adjustment aperture plate 360 a.FIG. 34A is a top view of an example of the aperture plate that isconstituted as a sliding type NA adjustment aperture plate 360 b, andFIG. 34B is a top view of an example of the aperture plate that isconstituted as a rotary type NA adjustment aperture plate 360 c.

In FIG. 34A, the NA adjustment aperture plate 360 b includes a pluralityof NA apertures 361, 362, and 363 having different diameters. Inaddition, the NA adjustment aperture plate 360 b includes a sliding typeNA adjusting aperture moving mechanism 365 on both sides in thelongitudinal direction. In this way, the plurality of NA apertures 361,362, and 363 are formed in the rectangular plate-like NA adjustmentaperture plate 360 b, and the sliding type NA adjusting aperture movingmechanism 365 enables movement in the horizontal direction. Thus, anaperture diameter and an NA aperture position in the NA adjustmentaperture plate 360 b can be adjusted according to the use. It ispossible to obtain an optimal sample surface image according to the typeor the use of the sample 200.

The sliding type NA adjusting aperture moving mechanism 365 may have,for example, a structure in which the NA adjustment aperture plate 360 bis sandwiched vertically by rail-like members, and a drive mechanismsuch as a linear motor is disposed, or a structure in which the NAadjustment aperture plate 360 b is sandwiched by rotary type railmembers, and a rotary type motor rotates the rotary type rail members.The sliding type NA adjusting aperture moving mechanism 365 may havevarious forms according to the use.

The NA adjustment aperture plate 360 c illustrated in FIG. 34B has aplurality of NA apertures 361 to 364 in the disc-like plate with arotary type NA adjusting aperture moving mechanism 366 disposed at thecenter thereof. The NA apertures 361 to 364 have different diameters.The NA aperture 361 has a largest diameter, the NA aperture 362 has asmaller diameter than the NA aperture 361, the NA aperture 363 has asmaller diameter than the NA aperture 362, and the NA aperture 364 has asmallest diameter

The rotary type NA adjusting aperture moving mechanism 366 uses a rotarytype motor or the like as a drive mechanism and may have a structure forswitching the aperture diameter of the NA adjustment aperture plate 360c by rotation.

According to the electro-optical inspection apparatus having thestructure illustrated in FIGS. 33, 34A, and 34B, the NA adjustmentaperture plates 360 a to 360 c are structured to be selectable among theplurality of NA apertures 361 to 364 and the position can be adjusted soas to support uses and types of the sample 200 flexibly. Thus, anoptimal contrast image can be obtained under various conditions. Notethat, the number of the NA apertures is not limited to that of thefigure, and any number of apertures may be provided.

FIG. 35 is a diagram illustrating an example of a structure of thedetector 400 of the electro-optical inspection apparatus illustrated inFIGS. 1 and 33, which is suitable for high resolution observation. Whenan electron direct incident type EB-CCD or EB-TDI is used as thedetector 400, compared with the conventional MCP, fiber optical plate(FOP), fluorescent screen, and TDI, an image having three times highercontrast than the conventional one can be obtained because nodeterioration occurs due to MCP and FOP transmission. In particular,when light from the bottom of the hole of the contact structure (202 inFIG. 26A) is detected, the spot (dot) becomes blurred in theconventional detector. In contrast, according to the detector 400illustrated in FIG. 35, high contrast can be obtained. In addition,because no deterioration of gain occurs due to use of MCP, unevenness ofluminance on the effective screen does not occur so that the exchangeperiod is long. Therefore, it is possible to reduce cost and time formaintaining the detector 400. In this way, the EB-CCD and the EB-TDI arepreferred for obtaining a high contrast image and in view of durability.

With reference to FIG. 35, an example of the form of using the EB-CCDand the EB-TDI is described. The detector 400 illustrated as an examplein FIG. 35 has a structure in which an EB-TDI 482 and an EB-CCD 481 areswitched so as to be exchanged according to the use. The EB-CCD 481 andthe EB-TDI 482 are electron sensors for receiving an electron beam, andthe electrons enter the detection surface directly. The EB-CCD 481 isused for optical axis adjustment of the electron beam and for adjustingand optimizing imaging conditions. On the other hand, when the EB-TDI482 is used, the EB-CCD 481 is moved away from the optical axis by amoving mechanism M, and imaging is performed by the EB-TDI 482 by usingconditions determined when the EB-CCD 481 is used or by referring to theconditions so that the sample surface is observed.

As described above, the detector 400 having the above-mentionedstructure can obtain an image of a semiconductor wafer by the EB-TDI 482using the electro-optical conditions determined when the EB-CCD 481 isused or referring to the conditions. It is also possible to evaluate adefect of the pattern by taking a review image using the EB-CCD 481after inspection of the sample surface by the EB-TDI 482. In this case,the EB-CCD 481 can accumulate images so that noise can be reduced. Thus,it is possible to take a review image of a defect detection part with ahigh S/N ratio. In this case, it is further effective to use the EB-CCD481 having a smaller pixel than the EB-TDI 482. In other words, it ispossible to take an image with a large number of pixels with respect toa size of the signal enlarged by a mapping projection optical system.Thus, an image for inspection or classification/determination of thetype of the defect or the like can be taken with higher resolution.

Note that, the EB-TDI 482 has a rectangular shape, for example, in whichpixels are arranged in a two-dimensional manner so as to receive theelectrons directly for forming an electron image. A pixel size thereofis 12 to 16 μm, for example. On the other hand, a pixel size of theEB-CCD 481 is 6 to 8 μm, for example.

In addition, the EB-TDI 482 is formed in a shape of a package 485. Thepackage 485 itself works as a feed-through, and pins 483 of the packageare connected to a camera 484 on the air side.

Adopting the structure illustrated in FIG. 35, it is possible toeliminate drawbacks such as an optical conversion loss due to the FOP,optical glass for hermetic seal, an optical lens, or the like,aberration and distortion in optical transmission, deterioration ofimage resolution due to the aberration and distortion, a detectionfailure, high cost, and a large scale.

As described above, as in the present invention, by utilizing the mirrorelectrons generated in the transition region, the electrons ec havingstructural information of the conductive region are separated from theelectrons ei having structural information of the insulation region, andthen an image is obtained under the condition where the luminance of theconductive region is higher than the luminance of the insulation region,or an image is obtained under the opposite condition where the luminanceof the insulation region is higher than the luminance of the conductiveregion. Thus, conspicuously higher contrast can be obtained than theimage obtained by sample observation without separating the electrons echaving structural information of the conductive region from theelectrons ei having structural information of the insulation region.

In addition, it is very effective to use the method and apparatusdescribed above with reference to FIG. 33 and further use the method andapparatus described above with reference to FIG. 35. In the method ofusing the EB-CCD or the EB-TDI, the deterioration factor due to thedetector can be reduced significantly. Therefore, it is possible toobtain an image with little deterioration of contrast and with highcontrast. Therefore, a variation of contrast of the image due to adifference of the NA position can be clearly known with high accuracywhen forming conditions for obtaining an image having high contrast bythe NA position adjustment or performing inspection. Therefore, the NAposition adjustment can be performed with high accuracy. Further,because a high contrast image can be obtained, inspection sensitivity inthe pattern inspection or the foreign matter inspection can beincreased. Therefore, in the apparatus including the SEM in the samechamber as illustrated in FIG. 2, it is possible to perform review of afiner defect in short time even if the defect review is performed basedon the inspection result. In addition, it is necessary to prevent dustor particles from adhering by using the apparatus, and it is veryeffective to use the method and apparatus illustrated in FIGS. 3 to 14as described above with reference to FIG. 33. The adhesion amount ofdust or particles increases only by introducing the sample to anotherapparatus for review or the like. If the same chamber is used, thenumber of times of conveying the sample and the number of times ofpassing through the load lock can be reduced, and operations of thestage can be reduced. Further, on the same stage, the position shift inthe review is small (⅕ to 1/20), and a period of time for searching fora defect position or the number of times of changing the field of view(FOV) can be reduced.

However, according to the study performed by the inventors of thepresent invention, it has been found that if the insulation region andthe conductive region are formed on the sample to be observed, and if itis necessary to detect both a short defect and an open defect on thesample surface with high accuracy, there could be a case where one typeof defect can be detected easily while the other type of defect can behardly detected only by obtaining an image under the condition where theluminance of the conductive region is higher than the luminance of theinsulation region, or obtaining an image under the opposite conditionwhere the luminance of the insulation region is higher than theluminance of the conductive region.

Specifically, if an image is obtained under the condition where theluminance of the conductive region is higher than the luminance of theinsulation region, there is a case where a short defect can be detectedeasily, but an open defect can be hardly detected. On the contrary, ifan image is obtained under the condition where the luminance of theinsulation region is higher than the luminance of the conductive region,an open defect can be detected easily, but a short defect can be hardlydetected.

Based on this knowledge, according to the sample observation method ofthe present invention, an image is obtained under the condition wherethe luminance of the conductive region is higher than the luminance ofthe insulation region, and another image is obtained under the conditionwhere the luminance of the insulation region is higher than theluminance of the conductive region. Then, based on those images, a shortdefect and an open defect on the sample surface are both detected withhigh accuracy.

In other words, in the sample observation method according to thepresent invention, the sample surface including the insulation regionand the conductive region is irradiated with the imaging electron beamhaving landing energy (LE) adjusted to the transition region in whichthe electrons having structural information of the sample surfaceinclude both the mirror electrons and the secondary electrons. Then,images of the sample surface irradiated with the imaging electron beamare taken under the condition where the luminance of the conductiveregion is higher than the luminance of the insulation region (ConditionA) and under the condition where the luminance of the insulation regionis higher than the luminance of the conductive region (Condition B).Note that, those images may be taken first under Condition A and thenunder Condition B, or first under Condition B and then under ConditionA.

FIGS. 36A to 36C are diagrams conceptually illustrating how the shortdefect and the open defect appear in the image obtained under thecondition where the luminance of the conductive region is higher thanthe luminance of the insulation region (Condition A) and the imageobtained under the condition where the luminance of the insulationregion is higher than the luminance of the conductive region (ConditionB). Here, the short defect is a state where there is a short in a partof the region formed in line of conductive material such as W or Cu(conductive region), and the open defect is a state where there is abreak (open) in a part of the region formed in line of conductivematerial (conductive region).

Specifically, Condition A and Condition B are realized by positionadjustment of the NA aperture plate 361 (see FIG. 1) so that manyelectrons ec having structural information of the conductive region areonly guided to the detector 400 or many electrons ei having structuralinformation of the insulation region are only guided to the detector400.

FIG. 36A is a diagram schematically illustrating the surface of thesample 200 including the conductive material region (conductive region)202 made of W, Cu, or the like and the insulation material region(insulation region) 203 made of SiO₂ or the like. Part (a) of FIG. 36Aillustrates a state where there is a short defect 204 in a part of theconductive material formed in line, and part (b) illustrates a statewhere there is an open defect 205 in a part of the conductive materialformed in line.

In addition, FIG. 36B is a diagram schematically illustrating images ofthe sample surface irradiated by the imaging electron beam, which areobtained under the condition where the luminance of the conductiveregion is higher than the luminance of the insulation region (ConditionA) by irradiating the above-mentioned sample surface with the imagingelectron beam having landing energy (LE) adjusted to the transitionregion in which the electrons having structural information of thesample surface include both the mirror electrons and the secondaryelectrons. Parts (a) and (b) of FIG. 36B correspond to parts (a) and (b)of FIG. 36A, respectively.

FIG. 36C is a diagram schematically illustrating images of the samplesurface obtained under the opposite imaging condition where theluminance of the insulation region is higher than the luminance of theconductive region (Condition B) so that contrast is reversed. Parts (a)and (b) of FIG. 36C correspond to parts (a) and (b) of FIG. 36A,respectively.

With reference to FIG. 36B, in the images obtained under the conditionwhere the luminance of the conductive region is higher than theluminance of the insulation region (Condition A), the luminance of theconductive region is relatively high, and hence the short defect isenhanced and is expressed in a larger size than the actual defect size(see part (a) of FIG. 36B). On the contrary, because the luminance ofthe insulation region is relatively low, the open defect is expressed ina smaller size than the actual defect size (see part (b) of FIG. 36B).

On the other hand, with reference to FIG. 36C, in the images obtainedunder the condition where the luminance of the insulation region ishigher than the luminance of the conductive region (Condition B), theluminance of the insulation region is relatively high, and hence theshort defect is expressed in a smaller size than the actual defect size(see part (a) of FIG. 36C). On the contrary, because the luminance ofthe conductive region is relatively low, the open defect is expressed ina larger size than the actual defect size (see part (b) of FIG. 36C).

The same phenomenon occurs also in a case where the defect isincomplete.

Part (a) of FIG. 37A illustrates a state where there is an incompleteshort defect 206 in a part of the conductive material formed in line,and part (b) of FIG. 37A illustrates a state where there is anincomplete open defect 207 in a part of the insulation material formedin line.

In addition, FIG. 37B is a diagram schematically illustrating images ofthe sample surface obtained under the above-mentioned irradiationcondition of the imaging electron beam where the luminance of theconductive region is higher than the luminance of the insulation region(Condition A). Parts (a) and (b) of FIG. 37B correspond to parts (a) and(b) of FIG. 37A, respectively.

In addition, FIG. 37C is a diagram schematically illustrating images ofthe sample surface obtained under the opposite imaging condition wherethe luminance of the insulation region is higher than the luminance ofthe conductive region (Condition B) so that contrast is reversed. Parts(a) and (b) of FIG. 37C correspond to parts (a) and (b) of FIG. 37A,respectively.

With reference to FIG. 37B, in the images obtained under the conditionwhere the luminance of the conductive region is higher than theluminance of the insulation region (Condition A), the luminance of theconductive region is relatively high, and hence the incomplete shortdefect is enhanced and is expressed in a larger size than the actualdefect size (see part (a) of FIG. 37B). On the contrary, because theluminance of the insulation region is relatively low, the incompleteopen defect is expressed in a smaller size than the actual defect size(see part (b) of FIG. 37B).

On the other hand, with reference to FIG. 37C, in the images obtainedunder the condition where the luminance of the insulation region ishigher than the luminance of the conductive region (Condition B), theluminance of the insulation region is relatively high, and hence theincomplete short defect is expressed in a smaller size than the actualdefect size (see part (a) of FIG. 37C). On the contrary, because theluminance of the conductive region is relatively low, the incompleteopen defect is expressed in a larger size than the actual defect size(see part (b) of FIG. 37B).

The reason why this phenomenon occurs is considered as follows.Specifically, when an image is obtained under the condition where theluminance of the conductive region is higher than the luminance of theinsulation region (Condition A), electrons emitted from the conductivematerial in the vicinity of a short defect or an open defect arediffused, and due to the action, the short defect part is imaged to bewider, while the open defect part is imaged to be narrower. On thecontrary, when an image is obtained under the condition where theluminance of the insulation region is higher than the luminance of theconductive region (Condition B), electrons emitted from a short defector an open defect are diffused, and due to the action, the short defectpart is imaged to be narrower, while the open defect part is imaged tobe wider.

In this way, an image is obtained under the condition where theluminance of the conductive region is higher than the luminance of theinsulation region, and another image is obtained under the conditionwhere the luminance of the insulation region is higher than theluminance of the conductive region. Thus, based on the images havingreverse contrast, both a short defect and an open defect on the samplesurface can be detected with high accuracy.

Hereinafter, description is given based on a specific example.

The sample used in this example has a pattern of line and space (L&S)similarly to that illustrated in FIGS. 36A to 36C and 37A to 37C. On thesurface of the sample, there are formed a region (conductive region) 202of Cu as conductive material and a region (insulation region) 203 ofSiO₂ as insulation material, and a width of line and a width of spaceare both 43 nm.

FIGS. 38A and 38B show results of experiment performed for determiningan optimal value of the landing energy (LE) of the imaging electron beamthat irradiates the sample surface. FIG. 38A is a table showing thelanding energy (LE), luminance values [DN] of the conductive materialand the insulation material, and the contrast. In addition, FIG. 38B isa graph of this table, in which the horizontal axis represents thelanding energy (LE), the left vertical axis represents the luminancevalues [DN] of the conductive material and the insulation material, andthe right vertical axis represents the contrast. Note that, imaging inthis case was performed by adjusting the center of the NA aperture 361of the NA adjustment aperture plate 360 (see FIG. 1) to substantiallythe same position as the center of orbit of the electron ec emitted fromthe conductive region 202. Note that, [DN] indicating gradationrepresents “Digital Number”, which expresses black and white gradationwith 8 bits and is pixel information in which DN=0 means black, whileDN=255 means white.

In this example, when the landing energy (LE) is 3.2 eV, the highestcontrast (0.41) is obtained.

FIGS. 39A and 39B show results of experiment performed for determiningan optimal value of dose of the charged electron beam that irradiatesthe sample surface. FIG. 39A is a table showing beam dose [mC/cm²],luminance values [DN] of the conductive material and the insulationmaterial, and the contrast. In addition, FIG. 39B is a graph of thistable, in which the horizontal axis represents the beam dose [mC/cm²],the left vertical axis represents the luminance values [DN] of theconductive material and the insulation material, and the right verticalaxis represents the contrast. Imaging in this case was also performed byadjusting the center of the NA aperture 361 of the NA aperture plate 360to substantially the same position as the center of orbit of theelectron ec emitted from the conductive region 202. The beam dose isdefined as a product of beam current density and irradiation time.

In this example, the contrast increases along with the dose, but thecontrast is saturated at a dose of approximately 2mC/cm². In otherwords, it is understood that it is sufficient if the dose of the chargedelectron beam to be irradiated for imaging with high contrast isapproximately 2mC/cm².

In the present invention, the electrons ec having structural informationof the conductive region are separated from the electrons ei havingstructural information of the insulation region so that high contrast isobtained. Thus, a short defect and an open defect are both detected withhigh sensitivity and high accuracy. Such separation between theelectrons ec having structural information of the conductive region andthe electrons ei having structural information of the insulation regioncan be performed by position adjustment of the NA aperture. Therefore,in the present invention, distributions of electrons from the conductiveregion and the insulation region of the sample surface are directlyobserved in an NA imaging mode, and hence the position adjustment of theNA aperture can be performed with high accuracy. Hereinafter, an exampleof a specific procedure is described.

The projection lens 370 disposed between the NA adjustment apertureplate 360 and the detector 400 was set to a predetermined voltage of5,500V, and a positional relationship at the position of the NAadjustment aperture plate 360 between distributions of the electrons echaving surface structural information of the conductive region 202 andthe electrons ei having surface structural information of the insulationregion 203 was checked in the NA imaging mode. Specifically, the dose ofthe charged electron beam was changed so as to check how much the changeof the dose caused a shift of the distribution state (center of orbit)of the electrons ei having surface structural information of theinsulation region 203 from the distribution state (center of orbit) ofthe electrons ec having surface structural information of the conductiveregion 202.

FIGS. 40A and 40B are diagrams illustrating results of positionconfirmation of the electron distribution in the NA imaging mode. FIG.40A is a table showing the beam dose [mC/cm²] and a shift of adistribution state of the electrons ei having surface structuralinformation of the insulation material 203, namely a shift from adistribution state of the electrons ec having surface structuralinformation of the conductive material 202, when being irradiated withthe charged electron beam of the dose. In addition, FIG. 40B is a graphof this table, in which the horizontal axis represents the beam dose[mC/cm²], and the left vertical axis represents a shift of thedistribution state of the electrons ei having surface structuralinformation of the insulation material 203. Here, the shift directionwas set to the Y direction. Note that, the shift of the distributionstate of the electrons ei indicated in the left vertical axis is anormalized value. The normalization of the shift was performed bysetting 0 as the position of the NA aperture transmitting the electronsfrom the conductive material, and setting 1 as the position of the NAaperture of the condition where the contrast was reversed. In addition,based on the results of the experiment for optimizing the dose of thecharged electron beam described above, an upper limit value of theirradiation amount of the charged electron beam was set to 2mC/cm².Further, as a reference, the same experiment was performed on a samplehaving an L&S width of 35 nm and a sample having an L&S width of 65 nm.

According to the results illustrated in FIGS. 40A and 40B, the dose ofthe charged electron beam is substantially proportional to a shift ofthe distribution state of the electrons ei having surface structuralinformation of the insulation region 203. Therefore, considering theresults of the experiment for optimizing the dose of the chargedelectron beam, it is understood that in order to separate the electronsec having structural information of the conductive region from theelectrons ei having structural information of the insulation region soas to obtain high contrast, the irradiation amount of the chargedelectron beam should be set to approximately 2mC/cm², and further the NAaperture 361 of the NA adjustment aperture plate 360 should be shiftedin the Y direction by a predetermined amount, so that imaging isperformed under the condition where the electrons ec having structuralinformation of the conductive region 202 are selectively guided to thedetector 400 and under the condition where the electrons ei havingstructural information of the insulation region 203 are selectivelyguided to the detector 400.

In addition, according to the results illustrated in FIGS. 40A and 40B,in the sample having a large wiring width (L&S width), a variation ofthe substrate potential (ΔV) becomes large because of a large volume ofthe insulation region. Therefore, the shift of the distribution of theelectrons ei having surface structural information of the insulationmaterial 203 is also large. On the contrary, as the wiring width (L&Swidth) decreases, the volume of the insulation material decreases.Therefore, a variation of the substrate potential (ΔV) becomes small sothat high contrast can be hardly obtained.

As described above, through the irradiation with he charged electronbeam, the electrons ec having structural information of the conductiveregion can be easily separated from the electrons ei having structuralinformation of the insulation region. As a result, high contrast can beobtained easily. This is because the irradiation with the chargedelectron beam causes a variation of the substrate potential (ΔV) so thatthe distribution of the electrons ei having surface structuralinformation of the insulation material is shifted. This means that theshift of the distribution of the electrons ei having surface structuralinformation of the insulation material can be estimated from thevariation of the substrate potential (ΔV).

FIGS. 41A and 41B show results of experiment performed for determiningan optimal value of the landing energy (LE) of the imaging electron beamirradiated to the sample surface in an electrified state. FIG. 41A is atable showing the landing energy (LE), luminance values [DN] of theconductive material and the insulation material, and the contrast. Inaddition, FIG. 41B is a graph of this table, in which the horizontalaxis represents the landing energy (LE), the left vertical axisrepresents the luminance values [DN] of the conductive material and theinsulation material, and the right vertical axis represents thecontrast. Note that, imaging in this case was also performed byadjusting the center of the NA aperture 361 of the NA adjustmentaperture plate 360 to substantially the same position as the center oforbit of the electron ec emitted from the conductive region 202.

Comparing FIG. 41B with FIG. 38B, it is understood that higher contrast(7.8) was obtained in the case where the sample surface in theelectrified state was irradiated with the imaging electron beam (seeFIG. 41B) than in the case where the sample surface in a non-electrifiedstate was irradiated with the imaging electron beam (see FIG. 38B). Thelanding energy (LE) corresponding to this is shifted to the low energyside. This is because, as described above, the substrate potentialchanged (by approximately 1V) because the insulation region of thesample surface was electrified, and as a result, the center of orbit ofthe electron ei omitted from the insulation region 203 was conspicuouslyshifted from the center of orbit of the electron ec emitted from theelectrified region 202, and hence the degree of separation between theelectrons ec having structural information of the conductive region andthe electrons ei having structural information of the insulation regionwas increased.

Therefore, it is possible to estimate the shift of the center of orbitof the electron ei emitted from the insulation region 203 by knowing inadvance how the optimal landing energy (LE) varies due to theelectrified state (substrate potential) of the sample surface. In otherwords, the shift of the center position of orbit of the electron ei canbe estimated from the substrate potential. Specifically, a shift of thesubstrate potential is read from a shift of the landing energy (LE)before and after the electrification. As described above, when theelectrified state changes, energy (speed) of the electron changes, andhence the force received when the electron passes through theelectromagnetic field generation means (E×B deflector) that is expressedby F=e·(v×B) also changes. Therefore, an orbit shift when the electronpasses through the E×B deflector can be calculated. Further, the shiftat the NA aperture position can be calculated from the orbit shift whenthe electron passes through the E×B deflector. Therefore, an actualshift of the center position of orbit of the electron ei can beverified.

FIGS. 42A and 42B are diagrams illustrating reverse of contrast by theNA aperture position adjustment. FIG. 42A is a table showing luminancevalues [DN] of the conductive material and the insulation material, andthe contrast, when the center position of the NA aperture was changedfrom substantially the same position as the center of orbit of theelectron ec emitted from the conductive region (normalized position of0) to a position in the Y direction (normalized position of 1.0). Inaddition, FIG. 42B is a graph of this table, in which the horizontalaxis represents the center position of the NA aperture [normalizedposition], the left vertical axis represents the luminance values [DN]of the conductive material and the insulation material, and the rightvertical axis represents the contrast. Note that, imaging in this casewas performed by irradiating the sample surface with the chargedelectron beam at 2mC/cm², with the center position of the NA aperturewhere the luminance of the conductive material became maximum being setas a normalized position of 0. Here, the “normalized position” means, asdescribed above, a relative coordinate when the NA aperture positionpassing through the electrons from the conductive material is set as 0while the NA aperture position where the contrast is reversed is set as1.

As illustrated in FIGS. 42A and 42B, as the NA aperture position isshifted in the Y direction from the normalized position of 0, theluminance of the conductive material is decreased while the luminance ofthe insulation material is increased. As a result, the contrast isdecreased gradually. Further, when the center position of the NAaperture is a normalized position of 0.6, the luminance of theconductive material is the same as the luminance of the insulationmaterial so that contrast cannot be obtained. As the NA apertureposition is further shifted in the Y direction, the luminance of theconductive material is further decreased while the luminance of theinsulation material is further increased. As a result, contrast isreversed and is increased gradually. In this way, by adjusting the NAaperture position, the contrast can be reversed.

FIG. 43 is a diagram conceptually illustrating the reverse of contrastdue to the NA aperture position adjustment. When the center position ofthe NA aperture is at substantially the same position as the center oforbit of the electron ec emitted from the conductive region (normalizedposition NP=0), the electrons ec are mainly guided to the detector. Asthe center position of the NA aperture is shifted in the Y direction,the amount of the electrons ec that can pass through the NA aperture isdecreased while the amount of the electrons ei that can pass through theNA aperture is increased. At a normalized position NP=0.6, the amountsof both the electrons become the same so that there is no difference ofluminance and contrast cannot be obtained. As the center position of theNA aperture is further shifted in the Y direction, the amount of theelectrons ec that can pass through the NA aperture is further decreasedwhile the amount of the electrons ei that can pass through the NAaperture is further increased. At a normalized position NP=1.0, theamounts of both the electrons are reversed so that the contrast isreversed.

FIG. 44 is a flowchart illustrating, by means of an example, a procedureof determining dependence on the dose of the electron orbit shift, and aprocedure of confirming the reverse of the material contrast, in thesample observation method of the present invention. Some steps have beendescribed above and hence details thereof are omitted.

First, the landing energy (LE) of the imaging electron beam is adjustedto the above-mentioned transition region (Step 102), and the samplesurface to be observed including the insulation region and theconductive region is irradiated with the imaging electron beam (Step103).

The NA aperture position is adjusted in the plane by the NA aperturemoving mechanism, and hence the center position of the NA aperture isadjusted to the center of orbit of the electron ec having structuralinformation of the conductive region (Step 104). Then, in this state,the landing energy (LE) of the imaging electron beam is adjusted so thata difference of luminance between the insulation region and theconductive region, namely the material contrast, becomes maximum (Step105).

Next, the sample surface is irradiated with the charged electron beamhaving a predetermined dose so that the insulation region is electrified(Step 106), and it is checked how much degree the center of orbit of theelectron ei from the insulation region in the electrified state isshifted at the NA aperture position (Step 107). After that, Step S106and Step 107 are repeated, to thereby determine dependence on the doseof the orbit shift of the electron ei from the insulation region in theelectrified state (Step 108).

When the dependence on the dose of the orbit shift of the electron eifrom the insulation region in the electrified state is determined (Yesin Step 108), an appropriate dose is determined based on the data (Step109).

After the appropriate dose is determined, the landing energy (LE) of theimaging electron beam is adjusted again. Specifically, the samplesurface is irradiated with the charged electron beam of the appropriatedose determined by the above-mentioned procedure, and in this state, thelanding energy (LE) for obtaining the maximum material contrast isdetermined (Step 110). Then, an image of the sample surface irradiatedwith the imaging electron beam of this landing energy (LE) is obtainedto measure the material contrast (Step 111). As described above inrelation to Step 107, the center position of the NA aperture in thiscase is at the center of orbit of the electron ec having structuralinformation of the conductive region. Therefore, the luminance of theobtained image is relatively high in the conductive region andrelatively low in the insulation region.

Next, the center position of the NA aperture is moved by the amount ofthe orbit shift of the electron ei when the irradiation with the chargedelectron beam of the appropriate dose is performed, so that the centerposition of the NA aperture coincides with the center of orbit of theelectron ei. Then, in this state, the material contrast is measuredagain (Step 112).

As described above, when this adjustment of the center position of theNA aperture is performed, the material contrast is reversed so that animage must be obtained in which the luminance of the insulation regionis relatively high while the luminance of the conductive region isrelatively low. Therefore, when the reverse of the material contrast isconfirmed (Yes in Step 113), the process is finished (Step 114). Whenthe reverse of the material contrast is not confirmed (No in Step 113),which means a certain problem has occurred in the procedure up to here,the process flow returns to Step 102 and the process is performed again.

According to the above-mentioned procedure, the dependence on the doseof the electron orbit shift is determined and the reverse of thematerial contrast is confirmed, thereby completing setting of conditionsnecessary for the sample observation of the present invention.

FIG. 45 is a flowchart illustrating, by means of an example, a procedureof the sample observation method of the present invention. Some stepshave been described above and hence details thereof are omitted.

The sample observation method according to a preferred aspect of thepresent invention includes Step 203 in which the sample surfaceincluding the insulation region and the conductive region is irradiatedwith the imaging electron beam having the landing energy (LE) forobtaining the maximum material contrast, and Steps 205 and 207 in whichthe electrons having structural information of the sample surfaceirradiated by the imaging electron beam are detected so that a samplesurface image is obtained. As described above, the landing energy (LE)of the imaging electron beam is adjusted to the transition region inwhich the electrons having structural information of the sample surfaceinclude both the mirror electrons and the secondary electrons. The stepsof obtaining the sample surface image include Step 205 in which an imageis obtained under the condition where the luminance of the conductiveregion is higher than the luminance of the insulation region, and Step207 in which an image is obtained under the condition where theluminance of the insulation region is higher than the luminance of theconductive region.

As described above, prior to Step 203 of irradiation with the imagingelectron beam, the sample surface is irradiated with the chargedelectron beam of an appropriate dose so that the insulation region iselectrified (Step 202). Then, the substrate potential is changed, and asa result, a shift between the center of orbit of the electron ei emittedfrom the insulation region and the center of orbit of the electron ecemitted from the electrified region is increased. The degree ofseparation between the electrons ec having structural information of theconductive region and the electrons ei having structural information ofthe insulation region is also increased. The above-mentioned appropriatedose is determined in advance in Step S109 as described above, and it ispreferred that the dose be set so that the electrification of theinsulation region by the irradiation with the electron beam issaturated.

In the state where the sample surface is irradiated with the imagingelectron beam in Step 203, the center position of the NA aperture isadjusted to the center of orbit of the electron ec having structuralinformation of the conductive region so that the material contrastbecomes maximum (Step 204). The image obtained under this condition isan image in which the luminance of the conductive region is relativelyhigh while the luminance of the insulation region is relatively low(Step 205).

Next, the center position of the NA aperture is adjusted to the centerof orbit of the electron ei having structural information of theinsulation region so that the material contrast becomes maximum (Step206). The image obtained under this condition is an image in which theluminance of the insulation region is relatively high while theluminance of the conductive region is relatively low (Step 207). Inother words, the image obtained under this condition has reversecontrast to the image obtained in Step 205.

Note that, the adjustment of the NA aperture position in Step 206 may beperformed so that the NA aperture position is adjusted by the amount ofthe orbit shift based on the orbit shift of the electron ei determinedin advance in Step 107.

FIG. 46 is a flowchart illustrating another example of the procedure ofthe sample observation method according to the present invention. Thisprocedure is different from the procedure illustrated in FIG. 45 inthat, after Step 305 in which an image is obtained under the conditionwhere the luminance of the insulation region is higher than theluminance of the conductive region, Step 307 is performed in which animage is obtained under the condition where the luminance of theconductive region is higher than the luminance of the insulation region.

In other words, the sample observation method according to this aspectincludes Step S303 in which the sample surface including the insulationregion and the conductive region is irradiated with the imaging electronbeam having the landing energy (LE) for obtaining the maximum materialcontrast, and Steps 305 and 307 in which the electrons having structuralinformation of the sample surface irradiated by the imaging electronbeam are detected so that a sample surface image is obtained. The stepsof obtaining the sample surface image include Step S305 in which animage is obtained under the condition where the luminance of theinsulation region is higher than the luminance of the conductive region,and Step S307 in which an image is obtained under the condition wherethe luminance of the conductive region is higher than the luminance ofthe insulation region.

Similarly to the procedure of FIG. 45, prior to Step 303 of irradiationwith the imaging electron beam, the sample surface is irradiated withthe charged electron beam of an appropriate dose so that the insulationregion is electrified (Step 302). Then, the substrate potential ischanged, and as a result, a shift between the center of orbit of theelectron ei emitted from the insulation region and the center of orbitof the electron ec emitted from the electrified region is increased. Thedegree of separation between the electrons ec having structuralinformation of the conductive region and the electrons ei havingstructural information of the insulation region is also increased.

In the state where the sample surface is irradiated with the imagingelectron beam in Step S303, the center position of the NA aperture isadjusted to the center of orbit of the electron ei having structuralinformation of the insulation region so that the material contrastbecomes maximum (Step 304). The image obtained under this condition isan image in which the luminance of the insulation region is relativelyhigh while the luminance of the conductive region is relatively low(Step 305).

Next, the center position of the NA aperture is adjusted to the centerof orbit of the electron ec having structural information of theconductive region so that the material contrast becomes maximum (Step306). The image obtained under this condition is an image in which theluminance of the conductive region is relatively high while theluminance of the insulation region is relatively low (Step 307). Inother words, the image obtained under this condition has reversecontrast to the image obtained in Step 305.

Note that, the adjustment of the NA aperture position in Step 306 may beperformed so that the NA aperture position is adjusted in the directionopposite to the shift direction by the amount of the orbit shift basedon the orbit shift of the electron ei determined in advance in Step 107.

As described above, when an image is obtained under the condition wherethe luminance of the conductive region is higher than the luminance ofthe insulation region, a short defect can be detected easily, but thereis a case where it is difficult to detect an open defect. In addition,on the contrary to this, when an image is obtained under the conditionwhere the luminance of the insulation region is higher than theluminance of the conductive region, an open defect can be detectedeasily, but there is a case where it is difficult to detect a shortdefect. Therefore, in order to detect both the short defect and the opendefect on the sample surface including the insulation region and theconductive region with high accuracy, it is not sufficient to obtain animage only under the condition where the luminance of the conductiveregion is higher than the luminance of the insulation region, or on thecontrary, to obtain an image only under the condition where theluminance of the insulation region is higher than the luminance of theconductive region.

According to the sample observation method of the present invention, animage is obtained under the condition where the luminance of theconductive region is higher than the luminance of the insulation region,and another image is obtained under the condition where the luminance ofthe insulation region is higher than the luminance of the conductiveregion. Thus, based on the images, both a short defect and an opendefect on the sample surface can be detected with high accuracy.

In other words, by using the sample surface image obtained by theabove-mentioned sample observation method according to the presentinvention, it is possible to detect presence or absence of a shortdefect with high sensitivity and high accuracy from the image obtainedunder the condition where the luminance of the conductive region ishigher than the luminance of the insulation region, and to detectpresence or absence of an open defect with high sensitivity and highaccuracy from the image obtained under the condition where the luminanceof the insulation region is higher than the luminance of the conductiveregion. Therefore, the method can be used also as a high-sensitivity andhigh-accuracy sample inspection method.

Hereinafter, an example is described in which the sample surface defectinspection was performed by the above-mentioned method.

A sample to be observed was prepared similarly to that illustrated inFIGS. 36A to 36C and 37A to 37C, having a line and space (L&S) patternof a region of Cu as conductive material (conductive region) and aregion of SiO₂ as insulation material (insulation region). Note that,the line width and the space width were both set to 43 nm. Various sizesof short defects and open defects were formed in a part of theconductive region of the L&S pattern, and those defects were detected.

When the sample observation was performed, an acceleration voltage ofthe electron source beam was set to −4,005V, and a surface potential ofthe sample 200 was set to −4,002.6V. Therefore, the landing energy (LE)of the imaging electron beam was 2.4 eV in the transition region inwhich the electrons having structural information of the sample surfaceincluded both the mirror electrons and the secondary electrons. Inaddition, the aperture diameter of the NA aperture 361 was set to 100 to300 μm, the insulation region was electrified by being irradiated withthe charged electron beam prior to imaging (electrified amount was 2mC/cm²), and current density of the imaging electron beam was set to 1mA/cm². Imaging was performed in this state. Note that, an inspectionpixel size for defect inspection was set to 29 nm square by setting themagnification of the electro-optical system lens. In addition, aninspection speed was set to 50 mega pixels per second (MPPS).

FIGS. 47A to 47C are tables showing results of the defect inspectionperformed in the above-mentioned condition. FIG. 47A is a table showingwhether or not a defect could be detected from the image obtained underthe condition where the luminance of the conductive region was higherthan the luminance of the insulation region. FIG. 47B is a table showingwhether or not a defect could be detected from the image obtained underthe condition where the luminance of the insulation region was higherthan the luminance of the conductive region. FIG. 47C is a table showingwhether or not a defect could be detected as a combination of theabove-mentioned two defect detection results. In those tables, a circlemeans that a defect could be detected, a cross means that a defect couldnot be detected, and a double circle means that a defect could bedetected in both inspections.

As understood from those results, according to the image obtained underthe condition where the luminance of the conductive region is higherthan the luminance of the insulation region, a short defect can bedetected with high accuracy, and on the other hand, according to theimage obtained under the condition where the luminance of the insulationregion is higher than the luminance of the conductive region, an opendefect can be detected with high accuracy. This means that an opendefect may be overlooked according to the image obtained under thecondition where the luminance of the conductive region is higher thanthe luminance of the insulation region, while a short defect may beoverlooked according to the image obtained under the condition where theluminance of the insulation region is higher than the luminance of theconductive region.

In contrast, as in the present invention, if it is determined whether ornot a defect exists from an image obtained under the condition where theluminance of the conductive region is higher than the luminance of theinsulation region and an image obtained under the condition where theluminance of the insulation region is higher than the luminance of theconductive region, both a short defect and an open defect having a sizelarger than at least 25 nm can be detected with high sensitivity andhigh accuracy.

The electro-optical inspection apparatus and the sample observationmethod of the present invention described above can be used, forinstance, in a semiconductor manufacturing process, for observation orinspection of a surface of a semiconductor wafer after processing thesemiconductor wafer. Using the electro-optical inspection apparatus andthe sample observation method according to the present invention forobserving the semiconductor wafer whose sample surface includes aninsulation region and a conductive region, an image with high contrastcan be obtained for inspecting quality of the semiconductor wafer. Thus,the electro-optical inspection apparatus and the sample observationmethod of the present invention can be effective means for manufacturinga semiconductor wafer without a defect. In this way, the electro-opticalinspection apparatus and the sample observation method according to thepresent invention can be used appropriately in a semiconductormanufacturing method.

Here, when a scanning type or mapping projection type electronmicroscope, namely an electro-optical inspection apparatus, is used forwiring inspection or defect inspection of a sample surface, the samplesurface may be charged up (electrified) due to friction with air duringair conveyance or irradiation with an electron beam in vacuum. When thecharge-up occurs on the sample surface, there is a problem that theelectron beam irradiating the sample surface is detected as beingaffected by the secondary electrons charged up in the sample, and hencean image of the sample is blurred.

As a measure against the above-mentioned problem that an image of thesample is blurred because the charge-up occurs on the sample surface,for example, there is proposed a method of inspecting a defect of asample as described in PCT 1999-046798 (Patent Document 5). In thismethod of inspecting a defect of a sample, a difference of distance tobe focused is converted into a charge-up amount on the sample. Inaddition, Japanese Patent Application Publication No. 2002-033068(Patent Document 6) discloses a sample defect inspection, in which ascanning type electron microscope is used, and a retarding voltage isapplied to the sample for suppressing the charge-up of the sample.

In a static electricity removing method for the charged-up sample,ionized gas in air or in a certain type of gas is usually used. However,in this static electricity removing method, there is a fear that thesample is charged up again after the removal of static electricity dueto friction with air during air conveyance. In addition, when removingstatic electricity due to the charge-up of the sample by the irradiationwith the electron beam in vacuum, it is also necessary to return thesample once to the air side, which is not efficient.

However, in the method disclosed in Patent Document 5, a map indicatinga difference of distance to be focused of the charged-up sample (voltagemap) is generated, and the focus of the charged-up sample is merelychanged based on the map. Therefore, static electricity due to thecharge-up on the sample surface is not removed. In addition, in themethod disclosed in Patent Document 6, in order to suppress thecharge-up of the sample due to the irradiation with the electron beam, aretarding voltage RTD is merely applied. Therefore, there is a fear thatthe sample surface is charged up again, and static electricity due tothe charge-up on the sample surface by natural electrification is notremoved.

Hereinafter, an inspection method for a sample surface according to thepresent invention is described, which is capable of efficiently removingstatic electricity due to the charge-up on the sample surface caused notonly by electrification of an electron beam but also by naturalelectrification of air.

First, a principle of setting potential distribution on the samplesurface according to an embodiment of the present invention is describedin detail.

FIG. 48 is a conceptual diagram illustrating a relationship among anacceleration voltage Vacc, the retarding voltage RTD, the landing energyLE, and the sample surface potential ΔV in inspection of the samplesurface according to the embodiment of the present invention. In FIG.48, the sample 200 is placed on the stage 100 of the electro-opticalinspection apparatus illustrated in FIG. 1 or 33 (not shown in FIG. 48),and the electron beam EB is irradiated from the electron gun 310 to thesample 200. In order to accelerate the electron beam generated from theelectron gun 310 with respect to the ground, a voltage of −4 to −7 kV,for example, is applied to the electron gun 310. This voltage isreferred to as an acceleration voltage Vacc. In addition, when a voltageof −4 kV, for example, is applied to the sample 200, the potential ΔV ofthe sample 200 viewed from the electron beam EB accelerated with respectto the ground is 0V if the acceleration voltage Vacc is −4 kV, and is −3kV if the acceleration voltage Vacc is −7 kV. The voltage to be appliedto the sample 200 is referred to as a retarding voltage RTD. A valueobtained by subtracting the retarding voltage RTD from the accelerationvoltage Vacc, namely the potential of the sample 200 viewed from theelectron beam EB accelerated with respect to the ground, is the landingenergy LE. This landing energy LE is expressed by Expression (2) below.

Landing energy LE=(Retarding Voltage RTD)−(Acceleration VoltageVacc)  (2)

However, the potential of the sample 200 is not always 0V depending onnatural electrification of the sample 200 or pre-irradiation of thesample 200 with an electron beam. Therefore, effective landing energyLEeff is expressed by Expression (3) below where ΔV represents thesample surface potential.

LEeff=LE+ΔV  (3)

In other words, the effective landing energy LEeff illustrated in FIG. 1can be expressed by Expression (4) below obtained by substitutingExpression (2) into Expression (3), as illustrated in FIG. 48.

Effective Landing Energy LEeff=(Retarding Voltage RTD)−(AccelerationVoltage Vacc)+(Sample Surface Potential ΔV)  (4)

FIG. 49 illustrates an example of a relationship between the effectivelanding energy LEeff illustrated in FIG. 48 and mean luminance meanDN onthe sample surface detected by irradiating the sample surface with theelectron beam. FIG. 49 illustrates a relationship between the meanluminance meanDN and the effective landing energy LEeff [eV] when thesample surface is irradiated with the electron beam EB while changingthe effective landing energy LEeff thereof from 0 to 7 eV, for example,and the electron beam EB coming back from the sample surface isconverted into brightness (luminance) as sample surface imageinformation. In FIG. 2, for example, it is supposed that the potentialof the sample 200 before being irradiated with the electron beam EB is aconstant value (here, 0 V, for example). The mean luminance meanDN whenthe sample surface is irradiated with the electron beam EB having theeffective landing energy LEeff of 0V is denoted by “A” in FIG. 49. Thismean luminance meanDN “A” is referred to as standard luminance, and theeffective landing energy LEeff corresponding to the standard luminance Ais referred to as a reference landing energy LE0. Here, the meanluminance meanDN of the sample surface is obtained by detecting theelectron beam coming back from the sample surface by reflection orexcitation by the electron beam irradiated to the sample surface andconverting the detected electron beam into luminance. This detectedelectron beam from the sample surface irradiated by the electron beamincludes secondary electrons emitted from the inside of the sample andmirror electrons reflected by the sample surface.

In the relationship between the effective landing energy LEeff and themean luminance meanDN illustrated in FIG. 49, if the mean luminancemeanDN of the sample surface is constant, the effective landing energyLEeff is constant. Then, the sample surface potential ΔV can bedetermined from Expression (4) described above. Note that, therelationship between the effective landing energy LEeff and the meanluminance meanDN illustrated in FIG. 49 may be determined, for example,by irradiating the electron beam having the effective landing energyLEeff to the insulation material region of the sample surface and byconverting the electron beam coming back from the sample surface intoluminance.

Next, with reference to FIG. 50, determination of the sample surfacepotential ΔV from the relationship between the effective landing energyLEeff and the mean luminance meanDN illustrated in FIG. 49 is described.FIG. 50 is a diagram illustrating a relationship between the samplesurface potential ΔV and the luminance difference ΔDN. In FIG. 50, thevertical axis represents the luminance difference ΔDN between thestandard luminance A when an arbitrary region of the sample surface isirradiated with the electron beam having the reference landing energyLE0 of 2.5 eV, for example, and the mean luminance meanDN when anarbitrary region of the sample surface is irradiated with the electronbeam having the landing energy LE. The horizontal axis represents thesample surface potential ΔV converted by the luminance difference ΔDN.

For instance, it is supposed that an arbitrary region of the samplesurface is irradiated with the electron beam, and mean luminancedistribution (luminance difference) ΔDN on the sample surface isdetected. Here, it is supposed that the luminance difference ΔDN of thearbitrary region of the sample surface is determined by the followingexpression. Luminance Difference ΔDN=(Mean Luminance meanDN)−(StandardLuminance A)

Then, the case where the mean luminance distribution (luminancedifference) ΔDN is positive, namely, the luminance difference ΔDN ishigher than the standard luminance A, and the case where the meanluminance distribution (luminance difference) ΔDN is negative, namely,the luminance difference ΔDN is lower than the standard luminance A arestudied. It is supposed that an arbitrary region of the sample surfaceis irradiated with the electron beam having the reference landing energyLE0 of 2.5 eV, for example. If the mean luminance meanDN is higher thanthe standard luminance A, it means that the sample surface potential ΔVis shifted to the negative side, namely, the sample surface iselectrified negatively as illustrated in FIG. 50. If the mean luminancemeanDN is lower than the standard luminance A, it means that the samplesurface potential ΔV is shifted to the positive side, namely, the samplesurface is electrified positively as illustrated in FIG. 50.Specifically, first, the luminance that is detected when the arbitraryregion of the sample surface is irradiated with the electron beam havingthe reference landing energy LE0 of, for example, 2.5 eV is regarded as100, for example, and the detected luminance of 100 is referred to asthe standard luminance A. Next, the arbitrary region of the samplesurface was irradiated with the electron beam whose arbitrary landingenergy LE was set to, for example, 3.5 eV, the luminance was 130. Inthis case, the luminance difference ΔDN between the standard luminance Aand the mean luminance meanDN is 30, the sample surface potential ΔV is−1 V from FIG. 50, and it is understood that the sample surface iselectrified negatively.

Next, with reference to FIG. 51, the luminance difference ΔDN isdescribed, which is detected when the effective landing energy LEeff ofthe electron beam irradiating an arbitrary region of the sample surfaceis adjusted. FIG. 51 is a diagram illustrating examples (a) to (d) whenthe effective landing energy LEeff of the electron beam irradiating thesample surface was changed. Note that, the examples (a) to (d) of FIG.51 are cases where the sample surface is an oxide.

The image of “WITHOUT PRE-DOSE” illustrated in (a) of FIG. 51 indicatesluminance of the sample surface detected when the arbitrary region ofthe sample surface was irradiated with only the electron beam having thereference landing energy LE0 of 2.5 eV. The luminance in this case isreferred to as standard luminance A. The landing energy of the electronbeam LE irradiating the arbitrary region of the sample surface in thiscase is the reference landing energy LE0.

The image of “3 eV” illustrated in (b) of FIG. 51 indicates luminance ofthe sample surface detected when the same region of the sample surfaceas in (a) of FIG. 51 was irradiated with the electron beam whosearbitrary landing energy LE was preset to 3 eV, and afterward irradiatedwith the electron beam whose reference landing energy LE0 was set to 2.5eV. In this case, the luminance is brighter than the standard luminanceA, and it is understood that the sample surface is electrifiednegatively.

The image of “8 eV” illustrated in (c) of FIG. 51 indicates luminance ofthe sample surface detected when the same region of the sample surfaceas in (a) of FIG. 51 described above was irradiated with the electronbeam whose arbitrary landing energy LE was preset to 8 eV, and afterwardirradiated with the electron beam whose reference landing energy LE0 wasset to 2.5 eV. In this case, the luminance is darker than the standardluminance A, and it is understood that the sample surface is electrifiedpositively.

Similarly, the image of “18 eV” illustrated in (d) of FIG. 51 indicatesluminance of the sample surface detected when the same region of thesample surface as in (a) of FIG. 51 was irradiated with the electronbeam whose arbitrary landing energy LE was preset to 18 eV, andafterward irradiated with the electron beam whose reference landingenergy LE0 was set to 2.5 eV. In this case, the luminance is darker thanthe standard luminance A, and it is understood that the sample surfaceis electrified positively. In this way, the potential ΔV of the samplesurface can be determined by comparing the standard luminance A detectedwhen being irradiated with the reference landing energy LE0 with theluminance detected when the effective landing energy LEeff is adjusted.

Next, with reference to FIG. 52, the determination of the sample surfacepotential ΔV is described, which is made based on the image information(luminance difference ΔDN) detected when the sample surface illustratedin (a) to (d) of FIG. 51 is irradiated with the electron beam whosearbitrary landing energy LE [eV] is set by Pre-Dose. Note that, thesample surface potential ΔV is determined from the luminance differenceΔDN illustrated in FIG. 50.

FIG. 52 is a diagram illustrating a change of the sample surfacepotential ΔV when an arbitrary region of the sample surface isirradiated with the electron beam while changing the arbitrary landingenergy LE, namely, when the “Pre-Dose” is performed and then theelectron beam whose reference landing energy LE0 is set is irradiated.In FIG. 52, first, the “Pre-Dose” is performed on an arbitrary region ofthe sample surface. When this “Pre-Dose” is performed, an arbitraryregion of the sample surface is irradiated with the electron beam whosearbitrary landing energy LE is set to 3, 8, 14, and 22 eV, for example.Next, the arbitrary region of the sample surface is irradiated with theelectron beam whose reference landing energy LE0 is set to 2.5 eV, forexample. The luminance difference ΔDN is determined from the meanluminance meanDN detected by the irradiation with the electron beamincluding the “Pre-Dose” and the standard luminance A. Then, using thisluminance difference ΔDN, the sample surface potential ΔV is determinedwith reference to FIG. 50.

As to the sample surface potential ΔV determined from the luminancedifference ΔDN illustrated in (a) to (d) of FIG. 51, it is understoodthat the landing energy LE that becomes brighter than the standardluminance A (electrified negatively) and the landing energy LE thatbecomes darker than the standard luminance A (electrified positively)are present when an arbitrary region of the sample surface is irradiatedin advance with the electron beam whose arbitrary landing energy LE isset, namely when the Pre-Dose is performed. From this, it is understoodthat a potential of the sample surface can be electrified positively ornegatively in advance by adjusting the landing energy LE of the electronbeam arbitrarily when being irradiated with the electron beam by thePre-Dose.

According to the above-mentioned result, the sample surface potential ΔVcan be electrified positively or negatively by changing the effectivelanding energy LEeff to be set for the electron beam irradiating thesample surface. Thus, it is possible to reset the electrified state ofan arbitrary region of the sample surface to a standard potential (or toan arbitrary potential state) by irradiating the region with theelectron beam having the luminance difference ΔDN obtained bysubtracting the standard luminance A, which is obtained when the samplesurface is irradiated with the electron beam having the referencelanding energy LE0, from the mean luminance meanDN, which is obtainedwhen the sample surface is irradiated with the electron beam having anarbitrary landing energy LE, namely the electron beam having the landingenergy LE that acts opposite electrification with respect to a result ofdetermination as to whether the sample surface is electrified positivelyor negatively. The following embodiment has a feature in that thefunction of removing static electricity of the electrification on thesample surface or setting a potential of the sample surface to anarbitrary potential using this principle is applied to an apparatus forinspecting a sample surface.

FIG. 53A is a diagram illustrating, as a brightness distribution, adistribution of the luminance difference ΔDN obtained when each regionof the sample surface is irradiated with the electron beam having anarbitrary landing energy LE, in which brightness (luminance differenceΔDN) distribution of each region is illustrated in the X-Y coordinatesystem. FIG. 53B illustrates distribution of the potential (ΔV) of eachregion of the sample surface converted from the luminance difference ΔDNof each region illustrated in FIG. 53A in the X-Y coordinate system. Inthe brightness distribution illustrated in FIG. 53A, luminance obtainedwhen each region of the sample surface is irradiated with the electronbeam having an arbitrary landing energy LE is regarded as the standardluminance A, and the luminance difference ΔDN indicating a differencebetween the standard luminance A and the mean luminance obtained wheneach arbitrary region of the sample surface is irradiated with theelectron beam having the effective landing energy LEeff is illustratedfor each region irradiated with the electron beam.

The luminance difference ΔDN of each region illustrated in FIG. 53A isdetermined, and a relationship between the sample surface potential ΔVand the luminance difference ΔDN illustrated in FIG. 50 is referred to.Thus, the luminance difference ΔDN of each region from the standardluminance A can be obtained as distribution of the sample surfacepotential ΔV. FIG. 53B illustrates a case where distribution of thepotential ΔV is −1V, 0V, +0.5V, and +1V, as a result of determination ofthe sample surface potential ΔV from the luminance difference ΔDN ofeach region illustrated in FIG. 53A.

Using position information (XY coordinates) of each region of the samplesurface and potential information of each region of the sample surfaceobtained from FIGS. 53A and 53B, and also using the potential of thesample surface that can be adjusted by the Pre-Dose illustrated in FIG.52, thereby irradiating the region in which the sample surface potentialΔV illustrated in FIG. 53B is +1V with the electron beam having thearbitrary landing energy LE for electrifying the potential of the samplesurface to −1V by the Pre-Dose, the region in which the potential ΔV is+1V can be set to 0V. Similarly, by irradiating other regionselectrified to potentials of −1V and +0.5V with the electron beam havingan arbitrary landing energy LE by the Pre-Dose, the other regions can bealso set to 0V. Further, in addition to setting each region of thepotential of the sample surface to 0V uniformly by the Pre-Dose, it ispossible to set each region of the potential of the sample surface to anarbitrary potential so as to set a uniform potential distribution.

In addition, by adjusting the effective landing energy LEeff of theelectron beam irradiating the sample surface by using theabove-mentioned Pre-Dose, it is possible to set the sample surface to adark field (electrified positively) or a bright field (electrifiednegatively). The sample surface is set to the dark field mainly forinspecting dust or particles (made of insulation material) on the sample(conductor such as Si or Cr). In this case, the entire sample surface isset to the dark field so that the dust or particles on the sampleglitter for detection.

FIG. 54 is a perspective view illustrating a specific example of thesample to be inspected. The sample illustrated in FIG. 54 is an examplein which a pattern portion 240 is formed on a substrate 230. If apattern inspection is mainly performed on this sample, it is necessaryto set the sample surface to the bright field. In the pattern inspectionof this sample, in order to detect black and white contrast forinspecting a defect or the like of the pattern portion 240 (for example,in the case of inspecting a top surface of the sample made of an oxideunder which there is a conductor containing mainly Cr or Si), theeffective landing energy LEeff of the electron beam irradiating theentire sample is adjusted so that the portion to be inspected has highbrightness according to the material to be detected as “white” (one ofdifferent materials constituting the pattern), namely so that theportion to be inspected is set to the bright field.

As described above, in the method of setting the potential distributionof the sample surface according to the embodiment of the presentinvention, the electron beam having an arbitrary landing energy LE isirradiated to scan the region in which the potential distribution of thesample surface should be known. Then, luminance of the region isdetected, and the luminance difference between the standard luminanceand the luminance of the scanned region is determined, to therebydetermine the (X,Y) distribution of the luminance difference ΔDN of eachscanned region. As to this (X,Y) distribution of the luminancedifference ΔDN, a difference from the standard luminance is determined,and hence it is possible to determine a shift of the landing energy LEfrom the reference landing energy LE0 corresponding to the standardluminance in a certain region, namely a variation of the potential ΔV[V] of the sample surface in a certain region. In addition, theabove-mentioned Pre-Dose may be performed according to the variation ofthe potential ΔV [V] of the sample surface so that the potentialdistribution of the sample surface can be adjusted.

Here, a principle of electrifying the sample surface potential ΔV to apositive potential or a negative potential is described. An electrondensity Je is calculated from an electron current value of the electrongun for generating the primary electron beam irradiating the samplesurface. Based on this current density Je and a blanking release time TS(time while the electron beam is irradiated) of a blanking signal (forstopping the electron beam), the dose of the sample surface is expressedby Expression (5) below. Note that, blanking of the blanking signalmeans that the primary electron beam is temporarily broken when thesample surface is not irradiated with the primary electron beam.

Dose=Js·τs  (5)

When sample surface information, for example, a thickness of resist (forexample, insulation material such as oxide) is denoted by d, and aspecific dielectric constant of the resist is denoted by ∈r, capacitanceC0 per unit area of the sample surface is expressed by Expression (6)below.

C0=∈r·∈0·S/d  (6)

In Expression (6), S denotes a unit area of 1 cm², and ∈0 denotes adielectric constant of vacuum.

In addition, because C0V=Q holds, Q is expressed by Expression (7)below.

Q=C0·ΔV  (7)

In Expression (7), Q denotes a total electron amount irradiating thesample surface. When the sample surface is irradiated with the electronbeam having the landing energy LE [keV], the total electron amount Q isexpressed by Expression (8) below, where η denotes a secondary electronemission ratio.

Q=Dose·(1−η)  (8)

Here, based on Expressions (7) and (8), the following expression holds.

Q=Dose·(1−η)=C0·ΔV

By solving this expression with respect to the secondary electronemission ratio η, Expression (9) below is obtained.

η=1−(C0·ΔV)/Dose  (9)

Expression (9) indicates that the secondary electron emission ratio η isuniquely related to a specific dielectric constant ∈r of the substanceforming the sample surface.

In other words, when Expression (6) is substituted into Expression (9)so as to solve with respect to the specific dielectric constant ∈r ofthe substance, a relationship between the secondary electron emissionratio η and the specific dielectric constant ∈r of the substance can beexpressed by Expression (10) below.

η=1−{(∈0·S·ΔV)/(d·Dose)}·∈r  (10)

In addition, as illustrated in FIG. 50, an increase of potential of thesample surface can correspond to the detected mean luminance. Therefore,the potential distribution of the sample surface can be known oppositelyfrom the distribution of the luminance difference ΔDN (cross sectionalgradation or the like) inspected from the electron beam irradiationcondition or the like.

Next, with reference to FIGS. 55A and 55B that are conceptual diagramsillustrating a model of transmittance of electrons through the sample inthe thickness direction, the transmittance is described.

First, with reference to FIG. 55A, there is described a case where thesecondary electron emission ratio η of the sample is smaller than 1. Asillustrated in FIG. 55A, if the amount of the secondary electronsemitted from the sample surface due to electrons entering the samplesurface is smaller than the amount of the entering electrons, the totalelectron amount Q accumulated inside the sample is negative as a whole.Therefore, when the amount of the electrons entering the sample surfaceis denoted by Dose_in, and the amount of the secondary electrons emittedfrom the sample surface is denoted by Dose_out, the total electronamount Q is expressed by Expression (11) below.

Q=Dose_in−Dose_out<0  (11)

Based on the relationship expressed in Expression (10), the secondaryelectron emission ratio η is expressed by Expression (12) below.

η=Dose_out/Dose_in  (12)

Based on Expression (11), a variation of the potential ΔV generated onthe sample surface is expressed by Expression (13) below.

Dose_in(1−η)<0  (13)

In addition, as illustrated in FIG. 55B, in relation to the electronenergy of the primary electron beam irradiated from the electron gun anda thickness of the sample, when a part of the primary electronspenetrates (passes through) the sample, the total electron amount Qaccumulated inside the sample is expressed by Expression (14) below,where the amount of the penetrating primary electrons is denoted byDose_th.

Q=Dose_in−Dose_out−Dose_th  (14)

Next, the transmittance α of the primary electrons is expressed byα=Dose_th/Dose_in. Then, the total electron amount Q that is accumulatedinside the sample is expressed by Expression (15) below.

Q=Dose_in(1−η−α)  (15)

Here, as to an increase of the sample surface potential ΔV, thetransmittance α can be expressed by Expression (16) below from arelationship between Expressions (15) and (7).

α=1−η−(ΔV·C0/Dose)  (16)

(where, Dose_th=Dose)

Q is 0 in the case of FIG. 55B, and hence the transmittance α can bedetermined by Expression (17) below.

α=1−η  (17)

The transmittance α is a function of landing energy LE of the electronbeam for irradiation and a thickness t of the sample (in particular, athickness of the resist), and hence an increase of the sample surfacepotential ΔV can be 0 under the condition satisfying f(LE, t)=1−η whereα=f(LE, t). Thus, an influence of the charge up (electrification) of thesample surface can be minimized. On the contrary, if the thickness t ofthe sample is known, the transmittance a can be controlled bycombination with the landing energy LE, and hence the condition can beused differently so that the sample surface is electrified positively iff(LE, t)=α>1−η holds, while the sample surface is electrified negativelyif f(LE, t)=α<1−η holds. Using this principle, it is possible toequalize the potential distributions by examining a potentialdistribution existing locally on the sample surface and by irradiatingwith the electron beam having the landing energy LE for canceling thepotential.

As described above, in a sample surface observation apparatus or asample surface inspection apparatus using an electron beam forinspecting a sample, energy of the electron beam irradiating the sampleis set according to physical properties of the surface materialoccupying most of the sample surface to be observed or inspected. Inthis setting, by setting the energy of the electron beam so that f(LE,t)=1−η holds as described above, an influence of electrification of thesample surface can be minimized so that a clear image or an inspectionresult with high sensitivity can be obtained. For instance, when theelectron beam irradiates a sample surface of a sample having regions ofdifferent thicknesses t made of the same material, if the secondaryelectron emission ratio η of the sample surface can be determined firstby irradiating the primary electron beam having a condition (α=0) suchthat the electron beam cannot penetrate absolutely, it is possible tocalculate the transmittance a of the electron beam in the region havinga small thickness t made of the same material (such thickness that theirradiated electron beam can penetrate). In addition, by using theabove-mentioned parameters such as the luminance difference (ΔDN), thedose, and the variation of the sample surface potential ΔV, it is alsopossible to examine the distribution of capacitance C of the samplesurface, the distribution of the secondary electron emission ratio η,and the distribution of the thickness t of the sample.

FIGS. 56 and 57 are diagrams schematically illustrating sampleobservation systems of second and third embodiments according to thepresent invention, in which potential distribution of the sample surfacecan be adjusted based on the method of adjusting the potential of thesample surface under the above-mentioned principle. FIG. 56 illustratesa structural example in the case where a mapping projection typeelectron microscope is used as the electro-optical inspection apparatus,and FIG. 57 illustrates a structural example in the case where ascanning electron microscope (SEM) is used as the electro-opticalinspection apparatus.

In the sample observation system illustrated in FIG. 56, a mappingprojection type electron microscope 2100 includes an electron beamgenerating source 2120 for generating a primary electron beam, a primaryelectro-optical system 2130 for guiding the primary electron beam to thesample 200, a secondary electro-optical system 2140 for guiding asecondary electron beam from the sample 200 due to irradiation with theprimary electron beam to an image sensor 2150, the image sensor 2150 forobtaining an image of the secondary electron beam from the sample 200due to irradiation with the primary electron beam, and an X-Y stage 2112on which the sample 200 is placed and which is capable of moving atleast in one direction, which are housed in vacuum chambers 2172, 2174,and 2176.

A thermal electron emission type electron gun 2132 is used as theelectron beam generating source 2120. This thermal electron emissiontype electron gun 2132 uses mainly lanthanum hexaboride (LaB₆), but itis possible to use a filament made of tungsten, or a cathode made of atungsten-based compound such as thoriated tungsten (Th—W) or tungstencarbide (W2C), or made of oxide such as (barium (Ba), strontium (Sr), orcalcium (Ca))CO₃.

The primary electro-optical system 2130 is means for guiding the firstelectron beam generated from the thermal electron emission type electrongun 2132 to the sample 200, and includes an aperture 2122 and anelectrostatic lens 2124.

The first electron beam generated from the thermal electron emissiontype electron gun 2132 has a circular, elliptical, or rectangular crosssection formed by the aperture 2122 and the electrostatic lens 2124 ofthe primary electro-optical system 2130, and is guided to the sample 200for irradiation. It is desired that a size (beam diameter) of the firstelectron beam formed in a circular, elliptical, or rectangular shape begenerally slightly larger than an element area of the TDI, the EB-TDI,the CCD, or the EB-CCD as the image sensor 2150. In addition, the sizeof the primary electron beam may be adjusted for each image sensor 2150,or may be set conforming to a size of the largest image sensor 2150.

As to the primary electron beam, a combination of the accelerationvoltage Vacc for accelerating to arbitrary energy in the primaryelectro-optical system 2130 and the retarding voltage RTD is adjusted soas to adjust the landing energy LE of the first electron beam when thesample 200 is irradiated. The acceleration voltage Vacc is adjusted byan acceleration voltage adjustment part 2162, for example, and theretarding voltage RTD is adjusted by a sample voltage adjustment part2166 disposed in the X-Y stage 2112, for example. The combination of theacceleration voltage Vacc for setting energy of the primary electronbeam and the retarding voltage RTD is changed according to desiredinformation obtained from the sample 200.

For instance, when a secondary electron image of the sample 200 isobtained, the acceleration voltage Vacc is set to 100 eV to a fewthousands eV, for example, and the retarding voltage RTD is set to a setvoltage of the secondary electro-optical system 2140 (straightpropagation condition of an E×B filter 2134 of the secondaryelectro-optical system 2140). In the case of obtaining an electron(mirror electron) image generated by perfectly elastic collision betweenthe primary electron beam irradiating the sample 200 and material of thesample 200, the retarding voltage RTD is adjusted. In addition, in thecase of obtaining an image of mirror electrons as reflection of theprimary electron beam that irradiates the sample and is reflected in thevicinity of the surface of the sample 200 due to an influence of theelectrified surface potential of the sample 200, the landing energy LEis set to 0 eV to a few tens eV. In other words, by changing thecombination of the acceleration voltage Vacc and the retarding voltageRTD, it is possible to obtain a relationship between the landing energyLE and the luminance difference as illustrated in FIG. 2.

The X-Y stage 2112 is a support table for supporting the sample 200 andcan move at least in the horizontal direction. The X-Y stage 2112 issupported on a vibration-preventing table 2114 so that vibration fromthe floor is not transmitted to the X-Y stage 2112 by action of thevibration-preventing table 2114. In addition, action of the X-Y stage2112 is controlled by an external stage control unit 2164. The X-Y stage2112 is provided with the sample voltage adjustment part 2166 foradjusting the retarding voltage RTD to be applied to the sample 200 asdescribed above. The retarding voltage RTD to be applied to the sample200 is adjusted so as to adjust the landing energy LE of the primaryelectron beam together with the acceleration voltage Vacc.

The secondary electro-optical system 2140 includes the E×B filter 2134and a plurality of electrostatic lenses 2136. In the case of the mappingprojection type electron microscope illustrated in FIG. 56, the primaryelectro-optical system 2130 is disposed obliquely to the optical axis ofthe secondary electro-optical system 2140. The primary electron beamgenerated from the thermal electron emission type electron gun 2132irradiates the sample 200 perpendicularly or substantiallyperpendicularly by action of the E×B filter 2134 constituted of anelectric field and a magnetic field, and the secondary electron beamcoming back from the sample 200 propagates straight through the E×Bfilter 2134 of the secondary electro-optical system 2140 in the verticaldirection in the figure so as to be guided to the image sensor 2150 byaction of the plurality of electrostatic lenses 2136. Note that, the E×Bfilter 2134 is included in both the primary electro-optical system 2130and the secondary electro-optical system 2140. Here, in the E×B filter2134, the magnetic field and the electric field are orthogonal. Theelectric field is denoted by E, the magnetic field is denoted by B, anda speed of a charged particle (electron beam in this embodiment) isdenoted by v. Then, the E×B filter 2134 allows only charged particlessatisfying the Wien condition of E=vB to propagate straight and bendsorbits of other charged particles. In other words, the E×B filter 2134generates a force FB due to the magnetic field and a force FE due to theelectric field with respect to the primary electron beam so that theorbit of the primary electron beam is bent and guided to the sample. Onthe other hand, with respect to the secondary electron beam, the E×Bfilter 2134 generates the force FB due to the magnetic field and theforce FE due to the electric field that act in opposite directions.Therefore, the forces are cancelled by each other, and hence thesecondary electron beam is guided to the image sensor 2150.

The image sensor 2150 can also perform scan imaging by time delayintegration (TDI). Before the TDI, there are disposed the micro channelplate (MCP) for amplifying the electron, the fluorescent screen forconverting the amplified electron into light, a fiber optic plate (FOP)for guiding the light to the TDI, and the like. In addition, instead ofthe TDI, it is possible to use the EB-TDI that can directly receive theelectrons (second electron beam) and convert the same to an image. Inaddition, in the case of taking a still image other than a scan image,it is possible to use a charge coupled device (CCD) instead of the TDIand to use an EB-CCD instead of the EB-TDI. Further, it is possible todispose the EB-CCD before the TDI so as to use the TDI for the scanimage and to use the EB-CCD for the still image. As the image sensor2150, various types of image sensors can be used, which can detect theelectrons (second electron beam) generated from the sample surfacesimultaneously by a plurality of pixels as a plane.

The image sensor 2150 is connected to a storage device 2152. The storagedevice 2152 is connected to a control part 2160. The control part 2160includes the retarding voltage adjustment part 2166 and the accelerationvoltage adjustment part 2162.

The X-Y stage control unit 2164 is controlled by the control part 2160so as to control the moving direction and the moving distance of the X-Ystage 2112 so that the surface of the sample 200 on the X-Y stage 2112is located at a desired position with respect to the irradiatingelectron beam.

Next to the vacuum chamber 2174 housing the X-Y stage 2112, there isdisposed a preliminary environmental chamber 2214 that can communicatewith the vacuum chamber 2174 via a gate valve 2218 that is opened andclosed. The preliminary environment chamber 2214 includes a temporarywaiting place 2216 for the sample 200 before and after the inspection towait. In addition, the preliminary environment chamber 2214 is providedwith a dry pump 2210 and a turbo molecular pump 2212 that can performvacuum evacuation so that the vacuum chambers 2172, 2174, and 2176 andthe preliminary environment chamber 2214 can be evacuated to vacuum.Note that, the turbo molecular pump 2212 and the dry pump 2210 mayfurther be disposed in each of the vacuum chambers 2172, 2174, and 2176as necessary.

The storage device 2152 stores sample surface image information obtainedby the image sensor 2150. The sample surface image information stored inthe storage device 2152 is output to the control part 2160. The controlpart 2160 controls the retarding voltage adjustment part 2166 and theacceleration voltage adjustment part 2162 so as to adjust the effectivelanding energy LEeff with respect to the primary electron beam, andcontrols the stage control unit 2164 so as to control a moving positionof the X-Y stage 2112 so that an arbitrary region of the sample surfaceis irradiated with the primary electron beam. The image sensor 2150detects the secondary electron beam coming back from the sample surface,and outputs the detected sample surface image to the storage device 2152to store the sample surface image. The storage device 2152 outputs thestored image to the control part 2160. In the control part 2160, apotential distribution determination part 2163 determines the potentialdistribution of the sample surface based on the sample surface imageinput from the storage device 2152, and a potential distributioncorrection part 2164 adjusts the potential distribution of the samplesurface to an arbitrary potential distribution based on the determinedpotential distribution.

The potential distribution determination part 2163 determines thepotential distribution of the surface of the sample 200 using the methoddescribed above as the principle. The potential distribution correctionpart 2164 adjusts the potential distribution of the surface of thesample 200 to an arbitrary potential distribution using the methoddescribed above as the principle.

Here, the adjustment method of the potential distribution of the samplesurface performed by the control part 2160 is described with referenceto a flowchart illustrated in FIG. 58. As illustrated in Step S401 ofFIG. 58, the retarding voltage adjustment part 2166 and the accelerationvoltage adjustment part 2162 perform adjustment of the effective landingenergy LEeff to be set for the primary electron beam irradiating thesample 200 to be inspected. The surface of the sample 200 is irradiatedwith the primary electron beam for which the effective landing energyLEeff is set, and the secondary electron beam coming back from thesurface of the sample 200 is detected by the image sensor 2150. Thedetected sample surface image is converted into the mean luminance. Thesample 200 to be inspected is conveyed from the temporary waiting place2216 of the preliminary environment chamber 2214 into the vacuum chamber2174 when the gate valve 2218 is opened and closed. Then, the surface ofthe conveyed sample 200 is irradiated with the primary electron beam forwhich the effective landing energy LEeff adjusted by the accelerationvoltage adjustment part 2162 and the retarding voltage adjustment part2166 is set. The irradiation of the primary electron beam having theeffective landing energy LEeff set therefor corresponds to theabove-mentioned Pre-Dose. The primary electron beam having the effectivelanding energy LEeff set therefor irradiates the region to be inspectedof the surface of the sample 200 or the entire region of the surface ofthe sample 200 with a magnification that is the same as themagnification specified by the inspection recipe (characteristic andmaterial of the sample (mask)). The secondary electron beam coming backfrom the sample 200 due to the irradiation of the primary electron beamis detected by the image sensor 2150, and the detected image isconverted into the mean luminance so that the luminance distributionhaving potential distribution and position information of the sample 200is obtained.

Next, the primary electron beam having the reference landing energy LE0set therefor irradiates the region to be inspected of the surface of thesample 200 or the entire region of the surface of the sample 200. Theluminance difference ΔDN is determined from the standard luminance A andthe mean luminance meanDN detected by the electron beam irradiationincluding the “Pre-Dose” described above, and the potential ΔV of theregion to be inspected or the entire region of the surface of the sample200 is determined from the graph of FIG. 50 using the luminancedifference ΔDN.

Next, in Step S402, as to the obtained luminance distribution of thesample 200, the potential distribution determination part 2163 of thecontrol part 2160 determines the luminance difference ΔDN from adifference between the mean luminance meanDN and the standard luminanceA of the sample surface. Then, with reference to the graph of FIG. 50,the potential ΔV is converted from the luminance difference ΔDN for eachregion to be measured of the surface of the sample 200.

Next, in Step S403, correction of the potential distribution of thesample 200 is performed, in which the retarding voltage adjustment part2166 and the acceleration voltage adjustment part 2162 adjust thelanding energy LE to cancel the potential of each region of the sample200 or to electrify the same to an arbitrary potential based on theobtained potential ΔV and the position information (X-Y coordinates) ofthe region to be measured of the surface of the sample 200. In StepS401, the sample surface is irradiated with the primary electron beamagain while the landing energy LE is adjusted for each region of thesample 200 irradiated with the primary electron beam, and hence thestatic electricity of the electrified sample 200 is removed or set to anarbitrary potential. The potentials of the inspection regions of thesample 200 are all equalized by the removal of static electricity orpotential setting, and a variation of the sensitivity due to adifference of the electrified state among the inspection regions of thesample hardly occurs in the image detected when being irradiated withthe primary electron beam. In addition, even in the case where thesample is inspected repeatedly, a variation of the potentialdistribution hardly occurs among the inspection regions.

When the sample 200 is inspected, an influence of the electrificationcan be removed again by the adjustment of the retarding voltage RTD. Inaddition, when the potential of the surface of the sample 200 isadjusted by the retarding voltage RTD, the dose to the sample can beknown from the current density of the electron gun and the inspectionspeed of the inspection apparatus. Therefore, an increase of potentialof the surface of the sample 200 can be determined in advance by oneinspection, and the effective landing energy LEeff can be constant bycorrecting the increase of potential by adjustment of the retardingvoltage RTD. In other words, the luminance difference ΔDN between themean luminance and the standard luminance of the surface of the sample200 is converted into the potential distribution, and the convertedpotential distribution is used so that the potential of the surface ofthe sample 200 can be set to be uniform (static electricity is removedto 0V), or can be set to an arbitrary potential (a positive potential ora negative potential).

Next, the case where the sample 200 to be inspected is exchanged or thesample 200 is inspected again is described. When the sample 200 isexchanged or inspected again, there are a case where the potentialdistribution of the sample surface is changed and further a case wherethe entire potential distribution of the sample surface is changed.Therefore, when the sample is exchanged or the same sample is inspectedagain, it is necessary to adjust the landing energy LE for eachinspection. In this case, luminance of an arbitrary region of thesurface of the sample 200 is checked, and using the luminancedistribution of the sample 200 described above, the landing energy LE isadjusted based on a difference between the mean luminance meanDN and thestandard luminance A obtained from the luminance distribution. Thus, thepotential distribution of the surface of the sample 200 can be adjustedagain to be uniform.

As described above, as to the effective landing energy LEeff, optimizedparameters other than the landing energy LE (for example, the NAposition and the size of the inspection apparatus, the Wien condition,and the current density) are set according to the inspection recipe(characteristics or the like of the sample (mask)). Thus, the inspectionwith good reproducibility can be realized.

Note that, the electro-optical inspection apparatus is used in a casewhere a defect of the sample surface pattern is inspected, in a casewhere dust or particles on the sample surface are detected, in a casewhere dust or particles on a multilayered film formed on the samplesurface or a portion having different thickness partially or locallyare/is detected, and further in a case where both shapes of a patternformed on the sample surface (see FIG. 54) and a pattern formed in amultilayered film are detected so that the sample potentials arecompared. In each case, the inspection can be performed with theeffective landing energy LEeff suitable for the inspection of the samplesurface, and the inspection can also be performed by the irradiationwith the charged particles (electron beam) having the landing energy LEof different combinations or the same combination a plurality of times.Note that, the electron beam to irradiate the sample surface is notlimited to a charged particle beam but can be a beam that generates apotential difference on the sample surface and can expect that theelectron beam comes back from the sample, for example, a high speed atombeam.

If the electron beam irradiates the sample surface a plurality of times,and if dust or particles on the sample are inspected, for example, theinspection is performed by irradiating the sample surface for the firsttime with the electron beam for which the effective landing energy LEeffis set to 10 eV to 30 eV, for example, so as to electrify slightlypositively based on information obtained from the potential distributionof the sample surface, and next irradiating the sample surface with theelectron beam for which the landing energy LE is set to 3.5 eV, forexample, so that the luminance of dust or particles on the sample can bemaximum. Then, dust or particles on the sample can be detected with highsensitivity.

In addition, when the sample surface pattern inspection is performed, ifthe sample surface is made of at last two types of materials, theinspection is performed in the following manner. The sample surface isirradiated for the first time with the electron beam for which theeffective landing energy LEeff is set to 2 eV to 7 eV, for example, sothat one of the materials becomes bright, namely to electrify to aslightly negative potential, based on information obtained from the“potential distribution of the sample surface” (see FIG. 50). Then, thelanding energy LE for the inspection is set so that a difference ofluminance between one of the materials and the other material generatedby the first irradiation, namely the contrast becomes maximum. Forinstance, the landing energy LE is set to 2 eV to 5 eV, and the electronbeam for which the above-mentioned landing energy LE is set irradiatesthe sample surface. Then, the potential distribution of the samplesurface can be inspected with high sensitivity.

The adjustment method of the potential distribution of the samplesurface illustrated in FIG. 58 can be performed also in the sampleobservation system illustrated in FIG. 2. In other words, if the systemcontrol part 950 of the system illustrated in FIG. 2 is structured to becapable of performing the same function as the control part 2160 of thesample observation system illustrated in FIG. 56, the potentialdistribution can be adjusted.

In the sample observation system illustrated in FIG. 57, a scanningelectron microscope (SEM) 3200 is used as the electro-optical inspectionapparatus as described above. The SEM 3200 includes a thermal electronemission type electron gun 3320 as the electron beam generating sourcefor generating the primary electron beam, a primary electro-opticalsystem 3300 for guiding the primary electron beam to the sample 200 tobe scanned, a secondary electro-optical system 3400 having a detector3100 for detecting the secondary electron beam coming back from thesample surface when the primary electron beam scans the sample surface,and the X-Y stage 2112 on which the sample 200 is placed and which iscapable of moving at least in one direction. Those components are housedin vacuum chambers 3720, 3740, and 3760, respectively.

The thermal electron emission type electron gun 3320 uses mainly LaB₆,but it is possible to use a filament made of tungsten, or a cathode madeof a tungsten-based compound such as Th—W or W2C, or made of oxide suchas Ba CO₃, Sr CO₃, or CaCO₃.

The primary electro-optical system 3300 is means for guiding the primaryelectron beam generated from the thermal electron emission type electrongun 3320 to the sample 200, and includes an E×B filter 3340, and aplurality of electrostatic lenses or electromagnetic lenses 3240. In thecase of the SEM 3200 illustrated in FIG. 57, the secondaryelectro-optical system 3400 is disposed obliquely to the optical axis ofthe primary electro-optical system 3300. The primary electron beamgenerated from the electron gun 3320 is condensed by the plurality ofelectromagnetic lenses 3240 to be a thin electron beam and irradiatesthe sample 200 perpendicularly or substantially perpendicularly byaction of the E×B filter 3340 constituted of an electric field and amagnetic field. The secondary electron beam coming back from the sample200 propagates straight through the E×B filter 3340 of the primaryelectro-optical system 3400 in the left direction in the figure so as tobe guided to the detector 3100. Note that, the E×B filter 3340 isincluded in both the primary electro-optical system 3300 and thesecondary electro-optical system 3400.

The secondary electro-optical system 3400 includes the detector 3100 fordetecting the secondary electron beam coming back from the samplesurface. As the detector 3100, a secondary electron multiplier tube ismainly used. The detector 3100 is connected to a control part 3160.

In FIG. 57, the element denoted by the same numeral or symbol as in FIG.56 is the same element as in FIG. 56, and detailed description thereofis omitted.

The sample observation systems of FIGS. 56 and 57 are used in a casewhere a defect of the pattern is inspected, in a case where dust orparticles on the sample are detected, in a case where dust or particleson a multilayered film formed on the sample or a portion havingdifferent thickness partially or locally are/is detected, and further ina case where both shapes of a pattern formed on the sample (see FIG. 54)and a pattern formed in a multilayered film are detected so that thesample potentials are compared. In each case, the inspection can beperformed with the effective landing energy LEeff suitable for theinspection of the sample surface, and the inspection can also beperformed by the irradiation with the charged particles (electron beam)having the landing energy LE of different combinations or the samecombination a plurality of times. In this case, the electron beam toirradiate the sample surface is not limited to a charged particle beambut can be a beam that generates a potential difference on the samplesurface and can expect that the electron beam comes back from thesample, for example, a high speed atom beam.

As described above, the foreign matter adhesion prevention method andthe electron beam inspection method of the present invention aredescribed with reference to various embodiments. According to theseforeign matter adhesion prevention method and the electro-opticalinspection apparatus of the present invention, dust or particles such asparticles coming toward the sample can be blocked by the dust collectingelectrode disposed to surround the periphery of the sample. Therefore,it is possible to prevent the dust or particles such as particles fromadhering to the sample surface. In addition, because adhesion of dust orparticles such as particles to the sample surface can be prevented, itis possible to perform inspection of, in particular, an ultrafinepattern of 100 nm or smaller, a structural evaluation, an enlargedobservation, a material evaluation, electrically conductive state, andthe like of the sample surface with high accuracy and high efficiency.

In addition, according to the present invention, even if an insulationregion and a conductive region are formed on the sample surface, a highcontrast image of the sample surface can be obtained, and it is easy toclassify a type of the defect (a short defect or an open defect). Inaddition, according to the present invention, static electricity due tocharge-up on the sample surface can be removed efficiently. Therefore,blurring of a sample image due to the charge-up can be prevented. Thus,together with an effect of preventing adhesion of the dust or particles,it is possible to perform inspection with very high accuracy.

While the present invention has been described above in detail withreference to the exemplary embodiments, it is to be understood that theinvention is not limited to the above-mentioned exemplary embodiments,and various modifications and replacement may be made thereto.

1. An electro-optical inspection apparatus for inspecting a surface of asample using an electron beam, comprising: an electron beam source; aprimary electro-optical system comprising at least a primary lens forinducing a primary electron beam emitted from the electron beam source;a stage for mounting the sample thereon, wherein the surface of thesample being irradiated with the primary electron beam induced throughthe primary electro-optical system; a secondary electro-optical systemcomprising at least a secondary lens and an aperture for defining NA(Numerical Aperture), for inducing secondary electrons and mirrorelectrons, the secondary electrons being emitted from the sample surfacewhen irradiating the sample surface with the primary electron beam, andthe mirror electrons being reflected from the sample surface and itsvicinity when irradiating the sample surface with the primary electronbeam; a detector for detecting at least either of the secondaryelectrons or mirror electrons induced through the secondaryelectro-optical system; a first power source for supplying a firstvoltage to the sample mounted on the stage; at lest a first electrodelocated to surround the sample mounted on the stage, for collectingdusts or particles; and a second power source for supplying a secondvoltage to the first electrode, wherein the second voltage has the samepolarity as that of the first voltage and an absolute value which isequal to and larger than that of the first voltage.
 2. Anelectro-optical inspection apparatus according to claim 1, furthercomprising: at least a second electrode located to surround the firstelectrode, for collecting dusts or particles; and a third power sourcefor supplying a third voltage to the second electrode, the third voltagehaving the same polarity as that of the first voltage and an absolutevalue which is equal to or larger than that of the first voltage.
 3. Anelectro-optical inspection apparatus according to claim 1, furthercomprising: a plate located over the sample mounted on the stage, tocover the sample, the plate having an aperture through which an electronbeam passes to/from the sample surface.
 4. An electro-optical inspectionapparatus according to claim 1, further comprising: a cover surroundingthe stage for preventing dusts or particles from flowing to the stage.5. An electro-optical inspection apparatus according to claim 1, furthercomprising: a first terminal plate comprising at least two terminals,one of which is connected to the first power source and the other ofwhich is connected to the second power source; a cable including twoelectrical wires, first ends of which are connected to the terminals ofthe first terminal plate, respectively; a box containing the terminalplate therein, a portion of the cable and a second electrode forcollecting dusts or particles in the box, the portion of the cable beingsupported as flexibly bending; and a second terminal plate fixed at thestage and comprising at least two terminals connected to second ends ofthe electrical wires, the terminals being used to supply the first andsecond voltages to the sample and the first electrode, wherein a portionof the cable between the box and the second plate is supported to extendlinearly, and the flexibly bending portion in the box bends or extendsas the stage is moving.
 6. An electro-optical inspection apparatus forinspecting a surface of a sample using an electron beam, comprising: anelectron beam source; a primary electro-optical system comprising atleast a primary lens for inducing a primary electron beam emitted fromthe electron beam source; a stage for mounting the sample thereon, thesurface of the sample being irradiated with the primary electron beaminduced through the primary electro-optical system; a secondaryelectro-optical system comprising at least a secondary lens and anaperture for defining NA (Numerical Aperture), for inducing secondaryelectrons and mirror electrons, the secondary electrons being emittedfrom the sample surface when irradiating the sample surface with theprimary electron beam, and the mirror electrons being reflected from thesample surface and its vicinity when irradiating the sample surface withthe primary electron beam; a detector for detecting at least ones of thesecondary electrons and mirror electrons induced through the secondaryelectro-optical system; a chamber capable of being evacuated andcontaining the stage therein; and a device for performing electrolyticdissociation gases in the chamber during a process of vacuuming thechamber to eliminate static electricity which exists on structures inthe chamber and materials on the structures.
 7. An electro-opticalinspection apparatus for inspecting a surface of a sample using anelectron beam, comprising: an electron beam source; a primaryelectro-optical system comprising at least a primary lens for inducing aprimary electron beam emitted from the electron beam source; a stage formounting the sample thereon, the surface of the sample being irradiatedwith the primary electron beam induced through the primaryelectro-optical system; a secondary electro-optical system comprising atleast a secondary lens and an aperture for defining NA (NumericalAperture), for inducing secondary electrons and mirror electrons, thesecondary electrons being emitted from the sample surface whenirradiating the sample surface with the primary electron beam, and themirror electrons being reflected from the sample surface and itsvicinity when irradiating the sample surface with the primary electronbeam; a detector for detecting at least ones of the secondary electronsand mirror electrons induced through the secondary electro-opticalsystem; and a chamber capable of being evacuated and containing thestage therein, inner walls of the chamber having at least a hole, orcomprising mesh-metallic plates attached thereto, the plates beingsupplied with a predetermined voltage.
 8. An electro-optical inspectionapparatus according to claim 1, the electron beam source emits a primaryelectron beam a cross section of which has a substantial area.
 9. Anelectro-optical inspection apparatus according to claim 8, furthercomprising: an energy control means for setting energy of the electronbeam directing to the sample surface and energy supplied to the samplesuch that electrons directing from the sample surface to a detectorwithin a transition band which contains mirror electrons and secondaryelectrons; and an aperture adjustment mechanism for adjusting a locationof at least an aperture on a plane perpendicular to an axis of asecondary electro-optical system of the inspection apparatus, so thatelectrons from a conductive material region of the sample surface andelectrons from a nonconductive material region of the sample surface areselectively induced to the detector.
 10. An electro-optical inspectionapparatus according to claim 9, wherein the secondary electro-opticalsystem of the inspection apparatus comprises a plurality of apertureshaving different diameters, respectively, the aperture adjustmentmechanism selects one of the apertures and adjusts its location suchthat electrons from either of the conductive material region and thenonconductive material region pass through the selected aperture to thedetector.
 11. An electro-optical inspection apparatus according to claim8, wherein the detector comprises EB-CCD(s) or EB-TDI(s).
 12. A methodof inspecting a surface of a sample using an electro-optical inspectionsystem, comprising the steps of: setting the sample on a stage;supplying a first voltage to the sample on the stage; supplying a secondvoltage to a first electrode located to surround the sample on the stageto collect dusts and particles, the second voltage having the samepolarity as that of the first voltage and an absolute value which isequal to or larger than that of the first voltage; emitting a primaryelectron beam from an electron beam source, and irradiating the samplesurface with the electron beam through a primary electro-optical system;and detecting, at a detector, at least either of secondary electrons ormirror electrons, the secondary electrons being emitted from the samplesurface when irradiating the sample surface with the primary electronbeam, and the mirror electrons being reflected from the sample surfaceand its vicinity when irradiating the sample surface with the primaryelectron beam.
 13. A method according to claim 12, further comprisingthe step of: supplying a third voltage to a second electrode located tosurround the first electrode, the third voltage having the same polarityas that of the first voltage and an absolute value which is equal to orlarger than that of the first voltage.
 14. A method of inspecting asurface of a sample using an electro-optical inspection apparatus,comprising the steps of: setting the sample on a stage; supplying afirst voltage to the sample on a stage; vacuuming a chamber containingthe stage; dissociating electrolyticaly gases in the chamber which haveexisted during the step of vacuuming the chamber to eliminate staticelectricity on structures in the chamber and materials on thestructures; emitting a primary electron beam from an electron beamsource, and irradiating the sample surface with the electron beamthrough a primary electro-optical system; and detecting, at a detector,at least ones of secondary electrons and mirror electrons, the secondaryelectrons being emitted from the sample surface when irradiating thesample surface with the primary electron beam, and the mirror electronsbeing reflected from the sample surface and its vicinity whenirradiating the sample surface with the primary electron beam.
 15. Amethod according to claim 12, wherein the electron beam source emits aprimary electron beam a cross section of which has a substantial area,and the method further comprises: setting energy of the electron beamdirecting to the sample surface and energy supplied to the sample suchthat electrons directing from the sample surface to a detector arewithin a transition band which contains mirror electrons and secondaryelectrons; and adjusting a location of an aperture defining NA(Numerical Aperture), on a plane perpendicular to an axis of thesecondary electro-optical system of the inspection apparatus, so thatelectrons from a conductive material region of the sample surface andelectrons from a nonconductive material region of the sample surface areselectively induced to the detector by the adjustment.
 16. A methodaccording to claim 15, wherein the secondary electro-optical systemcomprises a plurality of apertures having different diameters,respectively, and the step of adjusting comprises: selecting one of theapertures; and adjusting a location of the selected aperture such thatelectrons from either of the conductive material region and thenonconductive material region pass through the selected aperture to thedetector.
 17. An electro-optical inspection apparatus according to claim6, the electron beam source emits a primary electron beam a crosssection of which has a substantial area.
 18. An electro-opticalinspection apparatus according to claim 7, the electron beam sourceemits a primary electron beam a cross section of which has a substantialarea.